scsi: mpt3sas: Add Atomic RequestDescriptor support on Aero

If the Aero HBA supports Atomic Request Descriptors, it sets the Atomic
Request Descriptor Capable bit in the IOCCapabilities field of the IOCFacts
Reply message. Driver uses an Atomic Request Descriptor as an alternative
method for posting an entry onto a request queue.

The posting of an Atomic Request Descriptor is an atomic operation,
providing a safe mechanism for multiple processors on the host to post
requests without synchronization. This Atomic Request Descriptor format is
identical to first 32 bits of Default Request Descriptor and uses only 32
bits.

Signed-off-by: Suganath Prabu S <suganath-prabu.subramani@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>