drm/radeon: add some additional 6xx/7xx/EG register init

- SMX_SAR_CTL0 needs to be programmed correctly to prevent
problems with memory exports in certain cases.
- VC_ENHANCE needs to be initialized on 6xx/7xx.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/r600.c b/drivers/gpu/drm/radeon/r600.c
index f30dc95..bff6272 100644
--- a/drivers/gpu/drm/radeon/r600.c
+++ b/drivers/gpu/drm/radeon/r600.c
@@ -1839,6 +1839,7 @@
 	WREG32(PA_CL_ENHANCE, (CLIP_VTX_REORDER_ENA |
 			       NUM_CLIP_SEQ(3)));
 	WREG32(PA_SC_ENHANCE, FORCE_EOV_MAX_CLK_CNT(4095));
+	WREG32(VC_ENHANCE, 0);
 }