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/1467297225-21379-40-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_lrc.c

@@ -929,7 +929,10 @@ void intel_logical_ring_stop(struct intel_engine_cs *engine)
 
 	/* TODO: Is this correct with Execlists enabled? */
 	I915_WRITE_MODE(engine, _MASKED_BIT_ENABLE(STOP_RING));
-	if (wait_for((I915_READ_MODE(engine) & MODE_IDLE) != 0, 1000)) {
+	if (intel_wait_for_register(dev_priv,
+				    RING_MI_MODE(engine->mmio_base),
+				    MODE_IDLE, MODE_IDLE,
+				    1000)) {
 		DRM_ERROR("%s :timed out trying to stop ring\n", engine->name);
 		return;
 	}