drm/amd/powerplay: enable GPO

GPO is graphics power optimizer.
SMU calculates the 16 gfxclk V/F points according to the CU numbers
and memory activity.RLC picks one of them according to the memory
speed requirements for the data transmission.

Signed-off-by: Kenneth Feng <kenneth.feng@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>