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/1467297225-21379-34-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_dsi.c

@@ -279,7 +279,9 @@ static int dpi_send_cmd(struct intel_dsi *intel_dsi, u32 cmd, bool hs,
 	I915_WRITE(MIPI_DPI_CONTROL(port), cmd);
 
 	mask = SPL_PKT_SENT_INTERRUPT;
-	if (wait_for((I915_READ(MIPI_INTR_STAT(port)) & mask) == mask, 100))
+	if (intel_wait_for_register(dev_priv,
+				    MIPI_INTR_STAT(port), mask, mask,
+				    100))
 		DRM_ERROR("Video mode command 0x%08x send failed.\n", cmd);
 
 	return 0;