aacraid: SCSI blk tag support

aacraid: SCSI blk tag support

The method to allocate and free FIB's in the present code utilizes
spinlocks. Multiple IO's have to wait on the spinlock to acquire or free
fibs creating a performance bottleneck.

An alternative solution would be to use block layer tags to keep track
of the fibs allocated and freed. To this end aac_fib_alloc_tag was
created to utilize the blk layer tags to plug into the Fib pool.These
functions are used exclusively in the IO path. 8 fibs are reserved for
the use of AIF management software and utilize the previous spinlock
based implementations.

Signed-off-by: Raghava Aditya Renukunta <RaghavaAditya.Renukunta@pmcs.com>
Reviewed-by: Shane Seymour <shane.seymour@hpe.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>