drm/amdgpu: Add unique_id support for sienna cichlid

This is being added to SMU Metrics, so add the required tie-ins in the
kernel. Also create the corresponding unique_id sysfs file.

v2: Add FW version check, remove SMU mutex
v3: Fix style warning
v4: Add MP1 IP_VERSION check to FW version check

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