Add link to drmn device.

Sponsored by:	The FreeBSD Foundation
drm: Log error if we fail to attach fbd device
drm/radeon: Implement the FB_GETINFO() newbus callback
Fail to attach if fb_info not passed.

Sponsored by:	The FreeBSD Foundation
Fix copyrights.

Sponsored by:	The FreeBSD Foundation
Notify DRM about panic or kdb enter happen. So we can see kernel messages in
that case.
To investigate: Return from kdb is broken, seems due to locks usage. TODO

Sponsored by:	The FreeBSD Foundation