[SCSI] qla4xxx: IDC implementation for Loopback

Handle IDC Request Notify AEN and post IDC Acknowledgement
while participating in Loopback IDC.

Signed-off-by: Nilesh Javali <nilesh.javali@qlogic.com>
Signed-off-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>