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

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

ichwd: don't attach to isa pnp device(s) by accident

Reviewed by: imp, des
MFC after: 1 week

Add a driver for the watchdog timer function present on the LPC interface
bridge in Intel ICH-series chipsets.

The original implementation was by W. Daryl Hawkins of Texas A&M, but I
have made substantial modifications.