drm/i915: Only emit a flush request on the active ring.

When flushing the GPU domains,we emit a flush on *both* rings, even
though they share a unified cache. Only emit the flush on the currently
active ring.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -10,6 +10,10 @@ struct  intel_hw_status_page {
 struct drm_i915_gem_execbuffer2;
 struct  intel_ring_buffer {
 	const char	*name;
+	enum intel_ring_id {
+		RING_RENDER = 0x1,
+		RING_BSD = 0x2,
+	} id;
 	struct		ring_regs {
 			u32 ctl;
 			u32 head;