drm/radeon/kms: add info query for backend map

The 3D driver need to get the pipe to backend
map to certain things.  Add a query to get the
info.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/ni.c b/drivers/gpu/drm/radeon/ni.c
index 559dbd4..44c4750 100644
--- a/drivers/gpu/drm/radeon/ni.c
+++ b/drivers/gpu/drm/radeon/ni.c
@@ -833,6 +833,7 @@
 	rdev->config.cayman.tile_config |=
 		((gb_addr_config & ROW_SIZE_MASK) >> ROW_SIZE_SHIFT) << 12;
 
+	rdev->config.cayman.backend_map = gb_backend_map;
 	WREG32(GB_BACKEND_MAP, gb_backend_map);
 	WREG32(GB_ADDR_CONFIG, gb_addr_config);
 	WREG32(DMIF_ADDR_CONFIG, gb_addr_config);