drm/amd/pp: Use atombios api directly in powerplay (v2)

In order to remove the cgs wrapper functions for atombios api.

v2: squash in whitespace cleanup (Alex)

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