MFC r305600: amdsbwd.4: update supported hardware list

MFC r297386: Add support for AMD FCH watchdog timers.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

amdsbwd: update to support SB8xx southbridges

Many thanks to Tino <tinotom@gmail.com> for drawing my attention to
this, for doing a lot of testing and providing great feedback.
Many thanks to AMD for continuing to release public specifications for
their chipsets.

PR: kern/157568
Tested by: Tino <tinotom@gmail.com>
MFC after: 1 week

amdsbwd.4: fix history to reflect correct releases

Pointed out by: ru
MFC after: 4 days

amdsbwd.4: fix spelling of my name

Pointed out by: ru
MFC after: 3 days

amdsbwd: new driver for AMD SB600/SB7xx watchdog timer

The hardware is compliant with WDRT specification, so I originally
considered including generic WDRT watchdog support, but decided
against it, because I couldn't find anyone to the code for me.
WDRT seems to be not very popular.
Besides, generic WDRT porbably requires a slightly different driver
approach.

Reviewed by: des, gavin, rpaulo
MFC after: 3 weeks