drm/amdgpu: Add Unique Identifier sysfs file unique_id v2

Add a file that provides a Unique ID for the GPU.
This will persist across machines and is guaranteed to be unique.
This is only available for GFX9 and newer, so older ASICs will not
have this file in the sysfs pool

v2: Store it in adev for ASICs that don't have a hwmgr

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>