drm/amdgpu: Fix unique_id references for Sienna Cichlid

Since unique_id is only supported in PMFW 0x3A5300 and higher, we will
only be able to use it inside Smu_Metrics_V3_t, which requires PMFW
0x3A4900 and higher. Remove the unique_id/serial_number references from
the v1 and v2 tables to avoid any confusion, and return 0 if metrics_v1
or metrics_v2 are used to try to get the unique_id/serial_number.

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