[Development report #11] Audio Stack Improvements

MFC’d DEVFS_CDEVPRIV(9) and asynchronous device detach patches to
stable/14 earlier (would normally be after 2 months) after request from
re@ so that they can land in 14.1-BETA*, since the call-for-testing so
far has received positive feedback and things seem to work as expected.
Will send more call-for-testing emails once the 14.1-BETA1 is out
(around May 5).

Working on retiring the unit.* code in sound(4). See commit message in
review for more information: https://reviews.freebsd.org/D44912

Exchanging emails with some snd_hda(4) users who experience problems
with sound on their laptops (most likely pin-patching related issues as
usual).

Minor patches/clean up:
https://cgit.freebsd.org/src/commit/?id=d0032e6a9e6596302bf129d7f68a627a02c6cd0a
https://cgit.freebsd.org/src/commit/?id=41ab202ff74ea6af7e9125c9dfb430c729380f41
https://cgit.freebsd.org/src/commit/?id=4d2be7be3837d66ba242a0a7fd51632c3f89285d
https://cgit.freebsd.org/src/commit/?id=17969e696325273e250a1dc73f43de76c0836aae
https://cgit.freebsd.org/src/commit/?id=8b97dce6973ca1b6c3407c34c76d459f43ca1061
https://cgit.freebsd.org/src/commit/?id=a44c45c7f597d67d37e09396b0778a2847a30981
https://cgit.freebsd.org/src/commit/?id=1b82d425ec0ac155765bcdf706040534309e9c94

Closed https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=278319

Starting to sketch out oss(3). Needs careful planning.

This work is sponsored by the FreeBSD Foundation.

Christos