drm/radeon/dpm: add a late enable callback

Certain features need to be enabled after ring tests
(e.g., powergating, etc.).  Add a function pointer
to split out late enable features.

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

diff --cc drivers/gpu/drm/radeon/radeon.h
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_pm.c
Simple merge