drm/amd/amdgpu: Release xcp drm memory after unplug

Add a new API amdgpu_xcp_drm_dev_free().
After unplug xcp device, need to release xcp drm memory etc.

Co-developed-by: Jiang Liu <gerry@linux.alibaba.com>
Signed-off-by: Jiang Liu <gerry@linux.alibaba.com>
Signed-off-by: Meng Li <li.meng@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>