Retriving the horizontal timings from the port registers as part of
get_config().

This fixes a division by zero:

[   56.916557] divide error: 0000 [#1] PREEMPT SMP
[   56.921741] Modules linked in: i915(+) drm_kms_helper syscopyarea
sysfillrect sysimgblt fb_sys_fops drm intel_gtt agpgart cf
g80211 rfkill binfmt_misc ax88179_178a kvm_intel kvm irqbypass crc32c_intel
efivars tpm_tis tpm fuse
[   56.944106] CPU: 3 PID: 1097 Comm: modprobe Not tainted 4.6.0-rc4+ #433
[   56.951501] Hardware name: Intel Corp. Broxton M/RVP, BIOS
BXT1RVPA.X64.0131.B30.1604142217 04/14/2016
[   56.961908] task: ffff88007a854d00 ti: ffff88007aea0000 task.ti:
ffff88007aea0000
[   56.970273] RIP: 0010:[<ffffffffa01235b2>]  [<ffffffffa01235b2>]
drm_mode_hsync+0x22/0x40 [drm]
[   56.980043] RSP: 0018:ffff88007aea3788  EFLAGS: 00010206
[   56.985982] RAX: 000000000788b600 RBX: ffff880073c22108 RCX:
0000000000000000
[   56.993957] RDX: 0000000000000000 RSI: ffff88007ab06800 RDI:
ffff880073c22108
[   57.001935] RBP: ffff88007aea3788 R08: 0000000000000001 R09:
ffff880073c221e8
[   57.009903] R10: ffff880073c22108 R11: 0000000000000001 R12:
ffff88007a300000
[   57.017872] R13: ffff880073c22000 R14: ffff880175f78000 R15:
ffff880175f78798
[   57.025849] FS:  00007f105d3e6700(0000) GS:ffff88017fd80000(0000)
knlGS:0000000000000000
[   57.034894] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   57.041317] CR2: 00007f4d485101d0 CR3: 000000007a820000 CR4:
00000000003406e0
[   57.049292] Stack:
[   57.051539]  ffff88007aea37a0 ffffffffa043b632 ffff880175f787c8
ffff88007aea3810
[   57.059825]  ffffffffa043d59e ffff880175f787b0 ffff88007ab68c00
ffff88007aea37f0
[   57.068128]  ffff880073c221e8 ffff880073c22108 ffff880175f78780
ffff880100000000
[   57.076430] Call Trace:
[   57.079254]  [<ffffffffa043b632>] intel_mode_from_pipe_config+0x82/0xb0
[i915]
[   57.087405]  [<ffffffffa043d59e>] intel_modeset_setup_hw_state+0x55e/0xd60
[i915]
[   57.095847]  [<ffffffffa043ff94>] intel_modeset_init+0x8e4/0x1630 [i915]
[   57.103415]  [<ffffffffa047bcf0>] i915_driver_load+0xbe0/0x1980 [i915]
[   57.110745]  [<ffffffffa0116c19>] drm_dev_register+0xa9/0xc0 [drm]
[   57.117681]  [<ffffffffa011921d>] drm_get_pci_dev+0x8d/0x1e0 [drm]
[   57.124600]  [<ffffffff8195f942>] ? _raw_spin_unlock_irqrestore+0x42/0x70
[   57.132253]  [<ffffffffa03b0384>] i915_pci_probe+0x34/0x50 [i915]
[   57.139070]  [<ffffffff8149c375>] local_pci_probe+0x45/0xa0
[   57.145303]  [<ffffffff8149d300>] ? pci_match_device+0xe0/0x110
[   57.151924]  [<ffffffff8149d6cb>] pci_device_probe+0xdb/0x130
[   57.158355]  [<ffffffff81579b93>] driver_probe_device+0x223/0x440
[   57.165169]  [<ffffffff81579e85>] __driver_attach+0xd5/0x100
[   57.171500]  [<ffffffff81579db0>] ? driver_probe_device+0x440/0x440
[   57.178510]  [<ffffffff81577736>] bus_for_each_dev+0x66/0xa0
[   57.184841]  [<ffffffff815793de>] driver_attach+0x1e/0x20
[   57.190881]  [<ffffffff81578d6e>] bus_add_driver+0x1ee/0x280
[   57.197212]  [<ffffffff8157abc0>] driver_register+0x60/0xe0
[   57.203447]  [<ffffffff8149bc50>] __pci_register_driver+0x60/0x70
[   57.210285]  [<ffffffffa0119450>] drm_pci_init+0xe0/0x110 [drm]
[   57.216911]  [<ffffffff810dcd8d>] ? trace_hardirqs_on+0xd/0x10
[   57.223434]  [<ffffffffa023a000>] ? 0xffffffffa023a000
[   57.229237]  [<ffffffffa023a092>] i915_init+0x92/0x99 [i915]
[   57.235570]  [<ffffffff810003db>] do_one_initcall+0xab/0x1d0
[   57.241900]  [<ffffffff810f9eef>] ? rcu_read_lock_sched_held+0x7f/0x90
[   57.249205]  [<ffffffff81204f18>] ? kmem_cache_alloc_trace+0x248/0x2b0
[   57.256509]  [<ffffffff811a5eee>] ? do_init_module+0x27/0x1d9
[   57.262934]  [<ffffffff811a5f26>] do_init_module+0x5f/0x1d9
[   57.269167]  [<ffffffff8112392f>] load_module+0x20ef/0x27b0
[   57.275401]  [<ffffffff8111f8e0>] ? store_uevent+0x40/0x40
[   57.281541]  [<ffffffff81124243>] SYSC_finit_module+0xc3/0xf0
[   57.287969]  [<ffffffff8112428e>] SyS_finit_module+0xe/0x10
[   57.294203]  [<ffffffff81960069>] entry_SYSCALL_64_fastpath+0x1c/0xac
[   57.301406] Code: ff 5d c3 66 0f 1f 44 00 00 0f 1f 44 00 00 8b 87 d8 00 00
00 55 48 89 e5 85 c0 75 22 8b 4f 68 85 c9 78 1b 69 47 58 e8 03 00 00 99 <f7> f9
b9 d3 4d 62 10 05 f4 01 00 00 f7 e1 89 d0 c1 e8 06 5d c3
[   57.322964] RIP  [<ffffffffa01235b2>] drm_mode_hsync+0x22/0x40 [drm]
[   57.330103]  RSP <ffff88007aea3788>
[   57.334276] ---[ end trace d414224cb2e2a4cf ]---
[   57.339861] modprobe (1097) used greatest stack depth: 12048 bytes left

Fixes: 6f0e7535 ("drm/i915/BXT: Get pipe conf from the port registers")
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Acked-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461053894-5058-1-git-send-email-ramalingam.c@intel.com
(cherry picked from commit cefc4e18)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>