drm/radeon/kms: add dpm support for rs780/rs880

This adds dpm support for rs780/rs880 asics.  This includes:
- clockgating
- dynamic engine clock scaling
- dynamic voltage scaling

set radeon.dpm=1 to enable it.

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