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/1467297225-21379-16-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_display.c

@@ -1937,7 +1937,9 @@ static void ironlake_disable_pch_transcoder(struct drm_i915_private *dev_priv,
 	val &= ~TRANS_ENABLE;
 	I915_WRITE(reg, val);
 	/* wait for PCH transcoder off, transcoder state */
-	if (wait_for((I915_READ(reg) & TRANS_STATE_ENABLE) == 0, 50))
+	if (intel_wait_for_register(dev_priv,
+				    reg, TRANS_STATE_ENABLE, 0,
+				    50))
 		DRM_ERROR("failed to disable transcoder %c\n", pipe_name(pipe));
 
 	if (HAS_PCH_CPT(dev)) {