Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC: r227006, r227281, r227282

Add a PCI front-end to esp(4) allowing it to support AMD Am53C974 and
replace amd(4) with the former in the amd64, i386 and pc98 GENERIC kernel
configuration files. Besides duplicating functionality, amd(4), which
previously also supported the AMD Am53C974, unlike esp(4) is no longer
maintained and has accumulated enough bit rot over time to always cause
a panic during boot as long as at least one target is attached to it
(see PR 124667).

PR: 124667
Approved by: re (kib)
Obtained from: NetBSD (based on)

Add a PCI front-end to esp(4) allowing it to support AMD Am53C974 and
replace amd(4) with the former in the amd64, i386 and pc98 GENERIC kernel
configuration files. Besides duplicating functionality, amd(4), which
previously also supported the AMD Am53C974, unlike esp(4) is no longer
maintained and has accumulated enough bit rot over time to always cause
a panic during boot as long as at least one target is attached to it
(see PR 124667).

PR: 124667
Obtained from: NetBSD (based on)
MFC after: 3 days