m32r: Convert oaks32r irq chips

Convert the irq chips to the new functions and use proper flow
handlers. handle_level_irq is appropriate.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Cc: Paul Mundt <lethal@linux-sh.org>