drm/ttm: decrease ttm bo priority number

decrease and also reserve priority number for KFD using
Signed-off-by: Roger.He <Hongbo.He@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

include/drm/ttm/ttm_bo_driver.h

@@ -42,7 +42,7 @@
 #include <linux/spinlock.h>
 #include <linux/reservation.h>
 
-#define TTM_MAX_BO_PRIORITY	16U
+#define TTM_MAX_BO_PRIORITY	4U
 
 struct ttm_backend_func {
 	/**