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/1467297225-21379-41-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_lvds.c

@@ -231,7 +231,7 @@ static void intel_enable_lvds(struct intel_encoder *encoder)
 
 	I915_WRITE(ctl_reg, I915_READ(ctl_reg) | POWER_TARGET_ON);
 	POSTING_READ(lvds_encoder->reg);
-	if (wait_for((I915_READ(stat_reg) & PP_ON) != 0, 1000))
+	if (intel_wait_for_register(dev_priv, stat_reg, PP_ON, PP_ON, 1000))
 		DRM_ERROR("timed out waiting for panel to power on\n");
 
 	intel_panel_enable_backlight(intel_connector);