drm/amd/powerplay: add dummy pp table for raven. (v2)

As there is no PPTable in RV, it is difficult to
cleanly decouple PPTABLE functionality in existing
codes.

v2: agd: squash in clean build fix

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