drm/radeon: use hw generated CTS/N values for audio

Use the hw generated values rather than calculating
them in the driver.  There may be some older r6xx
asics where this doesn't work correctly.  This remains
to be seen.

See bug:
https://bugs.freedesktop.org/show_bug.cgi?id=69675

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