safexel manuals: Improve apropos and HW relnotes

safe.4:
Improve document description (Nd) for apropos. Remove Nm from sysctls
in synopsis. This was causing this page to get pulled into results for
apropos sysctl. Instead, use kernel declaration macros like vt(4).
Convert the HARDWARE tagged list to a column list for better rendering
in HW Relnotes. Tested in man(1) at MANWIDTH 59 and 80.

safexcel.4:
Nd: s/security packet/cryptographic offload/ for apropos.
HARDWARE: Create this section for inclusion in the HW relnotes.

SPDX: both tagged
MFC after: 3 days
MFC to: 13.5
Reported by: markj (cryptographic offload, Inside Secure)
Reviewed by: jhb, markj, mhorne
Accepted by: markj (src), mhorne (mentor)
Differential Revision: https://reviews.freebsd.org/D47706