drm/amd/powerplay: add interface to read pptable from vbios

This patch adds interface to read pptable from vbios for smu.

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