[SCSI] scsi_transport_fc: Introduce helper function for blocking scsi_eh

Move the duplicated code from FC LLDs to SCSI FC transport class.

Acked-by: James Smart <james.smart@emulex.com>
Acked-by: Giridhar Malavali <giridhar.malavali@qlogic.com>
Acked-by: Abhijeet Joglekar <abjoglek@cisco.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>