drm/i915: rename 'ring' where it refers to an engine or engine_id

'ring' is an old deprecated term for a GPU engine. Chris Wilson wants to
use the name for what is currently known as an intel_ringbuffer, but it
will be dreadfully confusing if some rings are ringbuffers but other
rings are still engines. So this patch changes the names of a bunch of
parameters called 'ring' to either 'engine' or 'engine_id' according to
what they actually are.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1469034967-15840-3-git-send-email-david.s.gordon@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_mocs.c b/drivers/gpu/drm/i915/intel_mocs.c
index 2280c32..bd46968 100644
--- a/drivers/gpu/drm/i915/intel_mocs.c
+++ b/drivers/gpu/drm/i915/intel_mocs.c
@@ -204,9 +204,9 @@
 	return result;
 }
 
-static i915_reg_t mocs_register(enum intel_engine_id ring, int index)
+static i915_reg_t mocs_register(enum intel_engine_id engine_id, int index)
 {
-	switch (ring) {
+	switch (engine_id) {
 	case RCS:
 		return GEN9_GFX_MOCS(index);
 	case VCS:
@@ -218,7 +218,7 @@
 	case VCS2:
 		return GEN9_MFX1_MOCS(index);
 	default:
-		MISSING_CASE(ring);
+		MISSING_CASE(engine_id);
 		return INVALID_MMIO_REG;
 	}
 }