[SCSI] qla4xxx: select iscsi boot sysfs attrs

qla4xxx now uses iscsi_boot_sysfs to export the targets used
for boot to sysfs. It needs to select that config option
to make sure that module is also built.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>