drm/i915: Replace open coded MI_BATCH_GTT

The (2<<6) virtual memory space selector harks back to gen3 and is
mandatory given our use of GTT space for batchbuffers. On gen4+, use of
the GTT became mandatory and bit6 marked reserved. However the code must
now explicitly set (1<<7), which conveniently is also (2<<6).

To clarify the meaning for future readers, replace the open coded (2<<6)
with MI_BATCH_GTT.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -231,6 +231,7 @@
 #define   MI_BATCH_NON_SECURE	(1)
 #define   MI_BATCH_NON_SECURE_I965 (1<<8)
 #define MI_BATCH_BUFFER_START	MI_INSTR(0x31, 0)
+#define   MI_BATCH_GTT		    (2<<6) /* aliased with (1<<7) on gen4 */
 #define MI_SEMAPHORE_MBOX	MI_INSTR(0x16, 1) /* gen6+ */
 #define  MI_SEMAPHORE_GLOBAL_GTT    (1<<22)
 #define  MI_SEMAPHORE_UPDATE	    (1<<21)

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -786,7 +786,8 @@ i965_dispatch_execbuffer(struct intel_ring_buffer *ring, u32 offset, u32 length)
 		return ret;
 
 	intel_ring_emit(ring,
-			MI_BATCH_BUFFER_START | (2 << 6) |
+			MI_BATCH_BUFFER_START |
+			MI_BATCH_GTT |
 			MI_BATCH_NON_SECURE_I965);
 	intel_ring_emit(ring, offset);
 	intel_ring_advance(ring);
@@ -823,7 +824,7 @@ i915_dispatch_execbuffer(struct intel_ring_buffer *ring,
 	if (ret)
 		return ret;
 
-	intel_ring_emit(ring, MI_BATCH_BUFFER_START | (2 << 6));
+	intel_ring_emit(ring, MI_BATCH_BUFFER_START | MI_BATCH_GTT);
 	intel_ring_emit(ring, offset | MI_BATCH_NON_SECURE);
 	intel_ring_advance(ring);