MFC kern: _umtx_op: compat32 refactoring

63ecb272: umtx_op: reduce redundancy required for compat32

All of the compat32 variants are substantially the same, save for
copyin/copyout (mostly). Apply the same kind of technique used with kevent
here by having the syscall routines supply a umtx_copyops describing the
operations needed.

umtx_copyops carries the bare minimum needed- size of timespec and
_umtx_time are used for determining if copyout is needed in the sem2_wait
case.

bd4bcd14: Fix !COMPAT_FREEBSD32 kernel build

One of the last shifts inadvertently moved these static assertions out of a
COMPAT_FREEBSD32 block, which the relevant definitions are limited to.

Fix it.

27a9392d: _umtx_op: fix robust lists after r367744

A copy-pasto left us copying in 24-bytes at the address of the rb pointer
instead of the intended target.

15eaec6a: _umtx_op: move compat32 definitions back in

These are reasonably compact, and a future commit will blur the compat32
lines by supporting 32-bit operations with the native _umtx_op.

60e60e73: freebsd32: take the _umtx_op struct definitions back

Providing these in freebsd32.h facilitates local testing/measuring of the
structs rather than forcing one to locally recreate them. Sanity checking
offsets/sizes remains in kern_umtx.c where these are typically used.

(cherry picked from commit 63ecb272a00c6f084a33db1c6ad3e925d4dcf015)
(cherry picked from commit bd4bcd14e3eae6f70790be65e862f89e2596b9af)
(cherry picked from commit 27a9392d543933f1aaa4e4ddae2a1585a72db1b2)
(cherry picked from commit 15eaec6a5c04b1cce7594cd1278600d7a57efc5a)
(cherry picked from commit 60e60e73fd9d185d62c36a499e21c124629eb8ba)