[SCSI] aacraid: add parameter to control FUA and SYNCHRONIZE_CACHE policy

aacraid.cache parameter, Disable Queue Flush commands:
        bit 0 - Disable FUA in WRITE SCSI commands
        bit 1 - Disable SYNCHRONIZE_CACHE SCSI command
        bit 2 - Disable only if Battery not protecting adapter supplied Cache

e.g.: aacraid.cache=7 will disable the FUA and SYNCHRONIZE_CACHE
commands if the adapter has reported that it's cache is battery backed
up.

This parameter permits experimentation with tradeoffs between
performance and caching policy.

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