drm/radeon: add support for Richland APUs

commit e4d170633fde379f39a90f8a5e7eb619b5d1144d upstream.

Richland APUs are a new version of the Trinity APUs
with performance and power management improvements.

Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>