drm/radeon: make audio_init consistent across asics

Call it in the asic startup callback on all asics.
Previously r600 and rv770 called it in the startup
and resume callbacks while all the other asics called
it in the startup callback.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>