drm/amdgpu:introduce new flag to identify VM domain for cntx_ctrl

To determine whether the context uses GPUVM or not.

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>