drm/amd/powerplay: clean up the APIs for pptable setup

Combine and simplify the logics for setup pptable.

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