ossl: Add a VAES-based AES-GCM implementation for amd64

aes-gcm-avx512.S is generated from OpenSSL 3.1 and implements AES-GCM.
ossl_x86.c detects whether the CPU implements the required AVX512
instructions; if not, the ossl(4) module does not provide an AES-GCM
implementation. The VAES implementation increases throughput for all
buffer sizes in both directions, up to 2x for sufficiently large
buffers.

The "process" implementation is in two parts: a generic OCF layer in
ossl_aes.c that calls a set of MD functions to do the heavy lifting.
The intent there is to make it possible to add other implementations for
other platforms, e.g., to reduce the diff required for D37421.

A follow-up commit will add a fallback path to legacy AES-NI, so that
ossl(4) can be used in preference to aesni(4) on all amd64 platforms.
In the long term we would like to replace aesni(4) and armv8crypto(4)
with ossl(4).

Note, currently this implementation will not be selected by default
since aesni(4) and ossl(4) return the same probe priority for crypto
sessions, and the opencrypto framework selects the first registered
implementation to break a tie. Since aesni(4) is compiled into the
kernel, aesni(4) wins. A separate change may modify ossl(4) to have
priority.

Sponsored by: Stormshield
Sponsored by: Klara, Inc.
Reviewed by: jhb
MFC after: 3 months
Differential Revision: https://reviews.freebsd.org/D39783