drm/i915: Move semaphore specific ring members to struct

This will be helpful in abstracting some of the code in preparation for
gen8 semaphores.

v2: Move mbox stuff to a separate struct

v3: Rebased over VCS2 work

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> (v1)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index ed30a5e..1e60f24 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2582,8 +2582,7 @@
 			if(ring == signaller)
 				continue;
 
-			if (sync_bits ==
-			    signaller->semaphore_register[ring->id])
+			if (sync_bits == signaller->semaphore.mbox.wait[ring->id])
 				return signaller;
 		}
 	}