scsi: qla2xxx: Move rport registration out of internal work_list

Currently, the rport registration is being called from a single work element
that is used to process QLA internal "work_list".  This work_list is meant for
quick and simple task (ie no sleep).  The Rport registration process sometime
can be delayed by upper layer.  This causes back pressure with the internal
queue where other jobs are unable to move forward.

This patch will schedule the registration process with a new work element
(fc_port.reg_work).  While the RPort is being registered, the current state of
the fcport will not move forward until the registration is done.  If the state
of the fabric has changed, a new field/next_disc_state will record the next
action on whether to 'DELETE' or 'Reverify the session/ADISC'.

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>