[SCSI] arcmsr: initial driver, version 1.20.00.13

arcmsr is a driver for the Areca Raid controller, a host based RAID
subsystem that speaks SCSI at the firmware level.

This patch is quite a clean up over the initial submission with
contributions from:

Randy Dunlap <rdunlap@xenotime.net>
Christoph Hellwig <hch@lst.de>
Matthew Wilcox <matthew@wil.cx>
Adrian Bunk <bunk@stusta.de>

Signed-off-by: Erich Chen <erich@areca.com.tw>
Signed-off-by: Adrian Bunk <bunk@stusta.de>