drm/amd/powerplay: append pptable for sienna_cichlid (v2)

Add function to append powerplay table from vbios for sienna_cichlid.

v2: squash in warning fix

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