[Development report #12] Audio Stack Improvements

Retired unit.*:
https://cgit.freebsd.org/src/commit/?id=25723d66369fe6786e9e4f5f77381b944755f267
https://cgit.freebsd.org/src/commit/?id=993d1fad5bd805dbd1820975e58839ff4276e7b0

Fixed a panic caused by 44e128fe9d92 ("sound: Implement asynchronous
device detach") (MFC'd both to stable/14 already):
https://cgit.freebsd.org/src/commit/?id=03614fcba25b9de99e69819bc4690f66a3d24438
https://cgit.freebsd.org/src/commit/?id=fa284525499d75955525839074bf5968d0923e6b

Fixed an existing NULL-dereference panic in dsp_clone() and
mixer_clone() (MFC'd both to stable/14 already):
https://cgit.freebsd.org/src/commit/?id=074d6fbebc160222cde6b726adcc7350881d7824
https://cgit.freebsd.org/src/commit/?id=b18b990d8e7b15d25243d85ea22374dfdde8a18b

Improving control flow and layering of pcm/ code:
https://cgit.freebsd.org/src/commit/?id=b3ea087c05d8c75978a302cbb3fa92ce1afa3e49
https://cgit.freebsd.org/src/commit/?id=a24050e2b784e13561da3ab731a1db92f2e3366c
https://cgit.freebsd.org/src/commit/?id=7cc1afc5589000ac6ad7a908b07fad3401367bd1
https://reviews.freebsd.org/D44993
https://reviews.freebsd.org/D44997
https://reviews.freebsd.org/D45015

Minor patches:
https://cgit.freebsd.org/src/commit/?id=e56c8996fc437488686e7cdef18258f16c5ea74e (MFC’d to stable/14)
https://reviews.freebsd.org/D44994
https://reviews.freebsd.org/D44998
https://reviews.freebsd.org/D44996
https://reviews.freebsd.org/D45013
https://reviews.freebsd.org/D45014
https://reviews.freebsd.org/D45016

Discussed with emaste@ and BigKnife on IRC about which PCI drivers we
can purge from sound(4). Sent an email to arch@ for wider discussion:
https://lists.freebsd.org/archives/freebsd-arch/2024-April/000641.html

Spent time researching and planning future deliverables.

This work is sponsored by the FreeBSD Foundation.

Christos