[SCSI] aacraid: improve queue balancing

The adapter queue is divided up equally to all the arrays to prevent
command starvation to any individual array. On the other hand,
physical targets are only granted a queue depth of one each. The code
prior to this patch used to deal with the incremental discovery of
targets, but the driver knows how many arrays are present prior to the
scan so this knowledge is used to generate a better estimate for the
queue depth.

Remove the capability of 'physical=0' from preventing access to the
class of adapters that have the RAID/SCSI mode of operation since none
of the physicals on the SCSI channel are candidates ever for an array.

As always, the user can override this default queue depth policy by
making the appropriate adjustments utilizing sysfs.

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