avr32: At32ap: Convert pop irq_chip to new functions

Also replace the open coded handler call with the proper wrapper.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
LKML-Reference: <20110206163009.190112353@linutronix.de>