drm/i915: Convert wait_for(I915_READ(reg)) to intel_wait_for_register()

By using the out-of-line intel_wait_for_register() not only do we can
efficiency from using the hybrid wait_for() contained within, but we
avoid code bloat from the numerous inlined loops, in total (all patches):

   text    data     bss     dec     hex filename
1078551    4557     416 1083524  108884 drivers/gpu/drm/i915/i915.ko
1070775    4557     416 1075748  106a24 drivers/gpu/drm/i915/i915.ko

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1467297225-21379-23-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_display.c

@@ -5721,7 +5721,9 @@ static void
 skl_dpll0_disable(struct drm_i915_private *dev_priv)
 {
 	I915_WRITE(LCPLL1_CTL, I915_READ(LCPLL1_CTL) & ~LCPLL_PLL_ENABLE);
-	if (wait_for(!(I915_READ(LCPLL1_CTL) & LCPLL_PLL_LOCK), 1))
+	if (intel_wait_for_register(dev_priv,
+				   LCPLL1_CTL, LCPLL_PLL_LOCK, 0,
+				   1))
 		DRM_ERROR("Couldn't disable DPLL0\n");
 
 	dev_priv->cdclk_pll.vco = 0;