scsi: megaraid_sas: Add 32 bit atomic descriptor support to AERO adapters

Aero adapters provides 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.

If Aero adapters support Atomic descriptor, driver should use it for
posting IOs and DCMDs to firmware.

Signed-off-by: Sumit Saxena <sumit.saxena@broadcom.com>
Signed-off-by: Chandrakanth Patil <chandrakanth.patil@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>