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

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

Add `siis` CAM driver for SiliconImage SiI3124/3132/3531 SATA2 controllers.

Driver supports Serial ATA and ATAPI devices, Port Multipliers
(including FIS-based switching), hardware command queues (31 command
per port) and Native Command Queuing. This is probably the second on
popularity, after AHCI, type of SATA2 controllers, that benefits from
using CAM, because of hardware command queuing support.

Approved by: re (kib)