drm/amdgpu/powerplay: implement interface pp_power_profile_mode

implement get_power_profile_mode for getting power profile mode status.

Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>