[RFC]: drm fixup redux

["Blair Sadewitz" <blair.sadewitz%gmail.com@localhost>]

Hello:

I'm looking for people to test my latest round of DRM patches.  The patch:

<ftp://ftp.NetBSD.org/pub/NetBSD/misc/bjs/patches/drm-bus_dma-and-mmap.diff>

The improvements (I hope!):

- Use the extent manager to track mappings and provide sane offset
"cookies" for mmap.  Now the radeon driver
   works on amd64!

- Use bus_dma for nearly all map types (carried over from prior patch).

- Plug some lock leaks in drm_bufs.c and remove superfluous locking in
drm_add_magic() (from git).

- Lower spl of mutexes to IPL_NONE (and so are now adaptive instead of
spin mutexes), save for irq_lock which is a spin mutex at IPL_VM.
  Use mutex_spin_enter()/mutex_spin_exit()  for irq_lock.

- This patch does not include the dma_lock rwlock() patches, as Eric
Anholt advised me the contention on this lock was not nearly
  high enough to warrant it.

I need some feedback before I can commit, so please do let me know how it goes!

Regards,

--Blair