[SCSI] qla2xxx: Support for asynchronous TM and Marker IOCBs.

Currently we can only issue the task management (TM)
commands via the mailbox mechanism. This is a limitation,
since only one mailbox command can be issued at a time.
The purpose of this effort is to provide support for
issuing and processing the respose to TM and Marker
IOCBs asynchronously. Towards achieving this, the
consolidated srb architecture that is currently used for
BSG and IOCB/Logio commands has been enhanced and used.

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