Needs the same compiler bug workaround as the kernel.

aes(9): Rewrite x86 SSE2 implementation.

This computes eight AES_k instances simultaneously, using the
bitsliced 32-bit aes_ct logic which computes two blocks at a time in
uint32_t arithmetic, vectorized four ways.

Previously, the SSE2 code was a very naive adaptation of aes_ct64,
which computes four blocks at a time in uint64_t arithmetic, without
any 2x vectorization -- I did it at the time because:

(a) it was easier to get working,
(b) it only affects really old hardware with neither AES-NI nor SSSE3
which are both much much faster.

But it was bugging me that this was a kind of dumb use of SSE2.

Substantially reduces stack usage (from ~1200 bytes to ~800 bytes)
and should approximately double throughput for CBC decryption and for
XTS encryption/decryption.

I also tried a 2x64 version but cursory performance measurements
didn't reveal much benefit over 4x32. (If anyone is interested in
doing more serious performance measurements, on ancient hardware for
which it might matter, I also have the 2x64 code around.)

Prompted by:

PR kern/59774: bearssl 32-bit AES is too slow, want 64-bit optimized
version in kernel

aes(9): New 64-bit bitsliced implementation.

Derived from BearSSL's aes_ct64 code. Compared to the aes_ct code,
on machines with native 64-bit integer arithmetic, aes_ct64 should
have approximately:

- the same throughput for:
. CBC encryption,
. CCM encryption/decryption, and
. CBC-MAC;

- double the throughput for:
. CBC decryption,
. XTS encryption/decryption.

(aes_ct computes AES on two blocks at a time; aes_ct64 computes it on
four blocks at a time, with roughly the same number of instructions.
CBC encryption and CBC-MAC are inherently sequential; CCM, being a
combination of CTR and CBC-MAC, can only really be parallelized two
ways, so having four ways available doesn't help; and CBC decryption
and XTS admit parallelism limited only by the size of the inputs.)

Enable with `options AES_BEAR64'. Should be a reasonable default on
all platforms with 64-bit integer registers. Caveat: uses about 1200
bytes of stack space. (Could approximately halve that, like the
BearSSL aes_ct code, at some speed cost which I haven't measured --
by moving the br_aes_ct64_skey_expand logic into add_round_key in
aes_ct64_{enc,dec}.c.)

PR kern/59774: bearssl 32-bit AES is too slow, want 64-bit optimized
version in kernel

aes(9): New aes_keysched_enc/dec.

These implement the standard key schedule. They are named
independently of any particular AES implementation, so that:

(a) we can swap between the BearSSL aes_ct and aes_ct64 code without
changing all the callers who don't care which one they get, and

(b) we could push it into the aes_impl abstraction if we wanted.

This eliminates all br_aes_* references outside aes_bear.c, aes_ct*.c,
and the new aes_keysched.c wrappers.

Preparation for:

PR kern/59774: bearssl 32-bit AES is too slow, want 64-bit optimized
version in kernel

introduce new GCC 12 warning disables and use them in a few places

this introduces 4 new warning disable flags:

CC_WNO_MISSING_TEMPLATE_KEYWORD
CC_WNO_REGISTER
CC_WNO_STRINGOP_OVERREAD
CC_WNO_ARRAY_BOUNDS

and documents them in README.warnings. of these, the string op
and array bounds are both problematic (real bugs) and also spurious
(not real bugs), and the other 2 are mostly temporary for older
3rd party code.

add some new uses of CC_WNO_STRINGOP_OVERFLOW.

fix m68k build for gallium and GCC 12.

Acknowledge clang warning for NEON cipher code on aarch64eb

We've already made the nonportable vector initializations portable; the
code works on aarch64eb.

Make the AES and ChaCha NEON tests work in softfloat userland.

(`Softfloat' here refers to the ABI, which of course may be running
on a CPU with NEON.)

Restrict the NEON code to v7hf - the softfloat toolchain does not like
it (nor is it likely to work if there is no FPU present).

Implement AES-CCM with ARMv8.5-AES.

Pass the requisite -msse options for i386.

New test sys/crypto/aes/t_aes.

Runs aes_selftest on all kernel AES implementations supported on the
current hardware, not just the preferred one.