drm/nouveau: use drm debug levels

- Use driver level (0x2) for NV_DEBUG instead of all levels
- Create a NV_DEBUG_KMS for KMS level (0x4) and use them in modesetting code
- Remove a few odd NV_TRACE calls and replace some of them with NV_DEBUG_KMS or
NV_INFO

Signed-off-by: Maarten Maathuis <madman2003@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>