[ARM] 3368/1: ixp4xx: set gpio direction in ixp4xx_config_irq

Patch from Alessandro Zummo

ixp4xx_config_irq did not configure the gpio line
as an input.

As an added bonus, the irq2gpio array has been converted
from int to char.

Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>