[ARM] 4022/1: iop13xx: generic irq fixups

* use irq_chip
* use handle_level_irq

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>