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/1467297225-21379-4-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.c

@@ -2568,13 +2568,15 @@ static int vlv_allow_gt_wake(struct drm_i915_private *dev_priv, bool allow)
 	I915_WRITE(VLV_GTLC_WAKE_CTRL, val);
 	POSTING_READ(VLV_GTLC_WAKE_CTRL);
 
-#define COND (!!(I915_READ(VLV_GTLC_PW_STATUS) & VLV_GTLC_ALLOWWAKEACK) == \
-	      allow)
-	err = wait_for(COND, 1);
+	err = intel_wait_for_register(dev_priv,
+				      VLV_GTLC_PW_STATUS,
+				      VLV_GTLC_ALLOWWAKEACK,
+				      allow,
+				      1);
 	if (err)
 		DRM_ERROR("timeout disabling GT waking\n");
+
 	return err;
-#undef COND
 }
 
 static int vlv_wait_for_gt_wells(struct drm_i915_private *dev_priv,