[SCSI] aacraid: add optional MSI support

Added support for MSI utilizing the aacraid.msi=1 parameter. This
patch adds some localized or like-minded janitor fixes. Since the
default is disabled, there is no impact on the code paths unless the
customer wishes to experiment with the MSI performance.

Signed-off-by: Mark Salyzyn <aacraid@adaptec.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>