[SCSI] qla2xxx: Add ISP24xx ISR routines.

Add ISP24xx ISR routines.

Add appropriate glue-code for ISP24xx support -- this
included generalizing some of the core handling
routines (qla2x00_async_event() [pull-up retrieval of
mailbox values] and qla2x00_status_entry()].  Fixup
2100/2300 ISRs to handle the new conventions.

Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>