drm/amdgpu/psp: initialize xgmi session (v2)

Setup and tear down xgmi as part of psp.

v2:
- make psp_xgmi_terminate static
- squash in:
drm/amdgpu: only issue xgmi cmd when it is enabled
drm/amdgpu/psp: terminate xgmi ta in suspend and hw_fini phase

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>