The pd/pt shadow bo will be used to backup page table, when gpu reset
happens, we can restore the page table by them.
V2:
Free shadow bo.
Signed-off-by: NChunming Zhou <David1.Zhou@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>