This should allow us to also support VRAM->GTT moves.

v2: fix missing vram_base_adjustment
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NHuang Rui <ray.huang@amd.com>
Tested-by: NPierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>