scsi: fnic: Add devcmd2 initialization helpers

This patch adds the devcmd2 wq initalization and devcmd2 ring allocation
helper interfaces used by devcmd2 init.

[mkp: typos]
Signed-off-by: Satish Kharat <satishkh@cisco.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>