[SCSI] aacraid: driver shutdown method

Add in pci shutdown method so that the adapter shuts down correctly and
flushes its cache. Shutdown should also disable the adapter's interrupt
when shutdown (in particularly if the driver is rmmod'd) to prevent
spurious hardware activities.

Signed-off-by: Mark Haverkamp <markh@osdl.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>