drm/amdgpu: Add memory partition id to amdgpu_vm

If xcp_mgr is initialized, add mem_id to amdgpu_vm structure to store
memory partition number when creating amdgpu_vm for the xcp. The xcp
number is decided when opening the render device, for example
/dev/dri/renderD129 is xcp_id 0, /dev/dri/rederD130 is xcp_id 1.

Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>