MFC r264794:
  Move xdev knobs from release/arm/release.sh and into an
  XDEV_FLAGS variable in ${KERNCONF}.conf file.

Local changes:
  Fix XDEV_FLAGS for stable/9 branch, in particular, remove
  all *_CLANG* knobs, and move WITH_GCC=1 to XDEV_FLAGS.
  This is effectively a no-op on stable/9, and merged for
  tracking purpose only.

Sponsored by:	The FreeBSD Foundation
MFC: r264832 (partial)

- Sprinkle const and static as appropriate.
- Convert the remainder of snd_hda(4) to take advantage of nitems().
- Use DEVMETHOD_END.
- Use NULL instead of 0 for pointers.