drm/amd/pm: Hide irrelevant pm device attributes

Change return code to EOPNOTSUPP for unsupported functions. Use the
error code information to hide sysfs nodes not valid for the SOC.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Asad Kamal <asad.kamal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>