For entering UMD stable Pstate, the operations to enter rlc_safe
mode, disable mgcg_perfmon and disable PCIE aspm are needed. And
the opposite operations should be performed on UMD stable Pstate
exiting.

V2: take those ASICs(CI/SI/VI) which may not support this into
    consideration
Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>