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/1467297225-21379-49-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -365,8 +365,11 @@ static void hsw_set_power_well(struct drm_i915_private *dev_priv,
 
 		if (!is_enabled) {
 			DRM_DEBUG_KMS("Enabling power well\n");
-			if (wait_for((I915_READ(HSW_PWR_WELL_DRIVER) &
-				      HSW_PWR_WELL_STATE_ENABLED), 20))
+			if (intel_wait_for_register(dev_priv,
+						    HSW_PWR_WELL_DRIVER,
+						    HSW_PWR_WELL_STATE_ENABLED,
+						    HSW_PWR_WELL_STATE_ENABLED,
+						    20))
 				DRM_ERROR("Timeout enabling power well\n");
 			hsw_power_well_post_enable(dev_priv);
 		}