David Brownell pointed out a mismatch in the avr32 extint code:
> I noticed a small glitch that's not fixed by this patch: the
> initial type is falling edge, but IRQ_TYPE_NONE is mapped to
> IRQ_TYPE_LEVEL_LOW. Potentially surprising.
Fix it by setting the initial type (and handler) to low level,
matching the meaning of IRQ_TYPE_NONE.
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>