drm/i915: Split i915_gem_flush_ring() into seperate invalidate/flush funcs

By moving the function to intel_ringbuffer and currying the appropriate
parameter, hopefully we make the callsites easier to read and
understand.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 55a94c1..6be1a89 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -707,14 +707,7 @@
 	/* Unconditionally invalidate gpu caches and ensure that we do flush
 	 * any residual writes from the previous batch.
 	 */
-	ret = i915_gem_flush_ring(ring,
-				  I915_GEM_GPU_DOMAINS,
-				  ring->gpu_caches_dirty ? I915_GEM_GPU_DOMAINS : 0);
-	if (ret)
-		return ret;
-
-	ring->gpu_caches_dirty = false;
-	return 0;
+	return intel_ring_invalidate_all_caches(ring);
 }
 
 static bool