drm/amdgpu: add shadow bo support V2

shadow bo is the shadow of a bo, which is always in GTT,
which can be used to backup the original bo.
V2:
reference shadow parent, shadow bo will be freed by who allocted him.

Signed-off-by: Chunming Zhou <David1.Zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/include/uapi/drm/amdgpu_drm.h b/include/uapi/drm/amdgpu_drm.h
index a902a60..5aef0b7 100644
--- a/include/uapi/drm/amdgpu_drm.h
+++ b/include/uapi/drm/amdgpu_drm.h
@@ -79,6 +79,8 @@
 #define AMDGPU_GEM_CREATE_CPU_GTT_USWC		(1 << 2)
 /* Flag that the memory should be in VRAM and cleared */
 #define AMDGPU_GEM_CREATE_VRAM_CLEARED		(1 << 3)
+/* Flag that create shadow bo(GTT) while allocating vram bo */
+#define AMDGPU_GEM_CREATE_SHADOW		(1 << 4)
 
 struct drm_amdgpu_gem_create_in  {
 	/** the requested memory size */