[SCSI] qla2xxx: Provide common framework for BSG and IOCB commands.

Currently, BSG and IOCB/Logio commands have a different
framework (srb structs). The purpose of this effort is to
consolidate them into a generalized framework for these
as well as other asynchronous operations in the future.

Signed-off-by: Giridhar Malavali <giridhar.malavali@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>