drm/amdgpu/gmc9: add a new gfxhub 1.1 helper for xgmi

Used to populate the xgmi info on vega20.

v2: PF_MAX_REGION is val - 1 (Ray)

Acked-by: Huang Rui <ray.huang@amd.com>
Acked-by: Slava Abramov <slava.abramov@amd.com>
Reviewed-by :Shaoyun liu <Shaoyun.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by :Shaoyun liu <Shaoyun.liu@amd.com>