Add xgmi pstate setting on powerplay routine.

V2: split the change of is_support_sw_smu_xgmi into a separate patch
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>