drm/amd/pm: drop navy_flounder hardcode of using soft pptable

Drop navy_flounder hardcode of using soft pptable, so that it
can use pptable from vbios when available.

Signed-off-by: Jiansong Chen <Jiansong.Chen@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>