The Intel Baytrail pinctrl driver implements irqchip callbacks which are
called with desc->lock raw_spinlock held. In mainline this is fine because
spinlock resolves to raw_spinlock. However, running the same code in -rt we
get:

 BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:917
 in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/0
 Preemption disabled at:[<ffffffff81092e9f>] cpu_startup_entry+0x17f/0x480

 CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.1.5-rt5 #13
  ...
 Call Trace:
  <IRQ>  [<ffffffff816283c6>] dump_stack+0x4a/0x61
  [<ffffffff81077e17>] ___might_sleep+0xe7/0x170
  [<ffffffff8162d6cf>] rt_spin_lock+0x1f/0x50
  [<ffffffff812e3b88>] byt_gpio_clear_triggering+0x38/0x60
  [<ffffffff812e3bc1>] byt_irq_mask+0x11/0x20
  [<ffffffff810a7013>] handle_level_irq+0x83/0x150
  [<ffffffff810a3457>] generic_handle_irq+0x27/0x40
  [<ffffffff812e3a5f>] byt_gpio_irq_handler+0x7f/0xc0
  [<ffffffff810050aa>] handle_irq+0xaa/0x190
  ...

This is because in -rt spinlocks are preemptible so taking the driver
private spinlock in irqchip callbacks causes might_sleep() to trigger.

In order to keep -rt happy but at the same time make sure that register
accesses get serialized, convert the driver to use raw_spinlock instead.

Also shorten the critical section a bit in few places.
Suggested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>