[ARM] 4275/1: generic gpio layer for ixp4xx

This patch brings generic gpio layer support to ixp4xx. It creates
functions needed for gpio->irq and irq->gpio translation.

It expects and initial value to be passed to
gpio_direction_output() which has been introduced by
commit 28735a72 in Linus git tree.

Generic gpio layer is going to be used by pxa2xx_udc driver.

Signed-off-by: Milan Svoboda <msvoboda@ra.rockwell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>