style.mdoc: HARDWARE generates Release Notes

FreeBSD Release Infrastructure has been building the Hardware
Release Notes from these subsections in the Kernel Interfaces Manual.
Standardize this behavior in the FreeBSD Manual page style guide with
everything we learned in the 14.2-RELEASE.

To me, this is an enormously exciting discovery, and I believe that
over the next 5 years, this can transform the supported hardware UX,
without reinventing the wheel, by doubling down on our ways instead
of reinventing them.

MFC after: 3 days
Reported by: bz (special thanks)
Reviewed by: imp, mhorne, pauamma, rpolaka
Approved by: mhorne (mentor)
Differential Revision: https://reviews.freebsd.org/D48343

(cherry picked from commit 29eb4de61a4c2ab1d940e10f3816db79e74d46b1)