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

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

Add the Areca SATA RAID driver (arcmsr). This supports the ARC-11xx and 12xx
series of controllers. Areca provides a CLI and HTTP management tool for
FreeBSD/i386 and FreeBSD/amd64 on their website. Many thanks to Areca for
their support of FreeBSD. Thanks also to Mike Tansca and Sentex Communications
for donating hardware.

Obtained from: Erich Chen <erich at areca com tw>