Add CDCLK specific display clock initialization sequence as per BSpec.

Note that the CDCLK initialization/uninitialization are done at their
current place only for simplicity, in a future patch - when more of the
runtime PM features will be enabled - these will be moved to power
well#1 and modeset encoder enabling/disabling hooks respectively. This
also means that atm dynamic power gating power well #1 is effectively
disabled.

The call to uninitialize CDCLK during system/runtime suspend will be
added later in this patchset.

v1: Added function definitions in header files
v2: Imre's review comments addressed
- Moved CDCLK related definitions to i915_reg.h
- Removed defintions for CDCLK frequency
- Split uninit_cdclk() by adding a phy_uninit function
- Calculate freq and decimal based on input frequency
- Program SSA precharge based on input frequency
- Use wait_for 1ms instead 200us udelay for DE PLL locking
- Removed initial value for divider, freq, decimal, ratio.
- Replaced polling loops with wait_for
- Parameterized latency optim setting
- Fix the parts where DE PLL has to be disabled.
- Call CDCLK selection from mode set

v3: (imre)
- add note about the plan to move the cdclk/phy init to a better place
- take rps.hw_lock around pcode access
- move DE PLL register macros here from another patch since they are
  used here first
- add BXT_ prefix to CDCLK flags
- add missing masking when programming CDCLK_FREQ_DECIMAL

v4: (ville)
- split the CDCLK/PHY parts into two patches, update commit message
  accordingly
- s/DISPLAY_PCU_CONTROL/HSW_PCODE_DE_WRITE_FREQ_REQ/
- simplify BXT_DE_PLL_RATIO macros
- fix BXT_DE_PLL_RATIO_MASK
- s/bxt_select_cdclk_freq/broxton_set_cdclk_freq/
- move cdclk init/uninit/set code from intel_ddi.c to intel_display.c
- remove redundant code comments for broxton_set_cdclk_freq()
- sanitize fixed point<->integer frequency value conversion
- use DRM_ERROR instead of WARN
- do RMW when programming BXT_DE_PLL_CTL for safety
- add note about PLL lock timeout being exactly 200us
- make PCU error messages more descriptive
- instead of using 0 freq to mean PLL off/bypass freq use 19200
  for clarity, as the latter one is the actual rate
- simplify pcode programming, removing duplicated
  sandybridge_pcode_write() call
- sanitize code flow, remove unnecessary scratch vars in
  broxton_set_cdclk() (imre)
- Remove bound check for maxmimum freq to match current code.
  This check will be added later at a more proper platform
  independent place once atomic support lands.
- add note to remove freq guard band which isn't needed on BXT
- add note to reduce freq to minimum if no pipe is enabled
- combine broxton_modeset_global_pipes() with
  valleyview_modeset_global_pipes()

Signed-off-by: Vandana Kannan <vandana.kannan@intel.com> (v2)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>