drm/amd/powerplay: add UMD P-state in powerplay.

This feature is for UMD to run benchmark in a
power state that is as steady as possible. kmd
need to fix the power state as stable as possible.
now, kmd support four level:
profile_standard,peak,min_sclk,min_mclk

move common related code to amd_powerplay.c

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>