DragonFlyBSD

During sound configuration problems (which turned out to be usual error
between keyboard and chair) I updated sound code to the latest one from
FreeBSD RELENG_6. It didn't help me (obviously), but I realised it
should help a lot of hda users and also contains the new envy24 driver,
so I continued work on it.

Only ich is tested briefly by me and hda is tested by josepht from
#dragonflybsd. So, I'd say that there is good chance it doesn't blow up
your system ;). More tests (especially hda and envy24) are very welcome.

Don't pay attention to tags etc, this cleanup will follow before commit.

There were two problems I'm not sure though that I handled correctly.

• New experimental polling mode using simple callout_* mechanism uses
  callout_drain() we don't have in df. I used callout_stop() instead,
  but as I'm not familiar with this mechanism, I'm not sure at all.
  Polling isn't enabled by default, so it shouldn't bite testers anyway.
• AFAICS we don't have uncacheable DMA support, so PCI snooping is used.
  I'm not sure I handled all related stuff correctly (grep for
  BUS_DMA_NOCACHE from patch).

The rest of it should be quite straightforward.

http://hasso.linux.ee/stuff/patches/dragonfly/sound-latest-fbsd6.patch.txt