[ARM] 4961/1: gpiolib support for SA-1100 architecture

This adds gpiolib support for the SA-1100 arch:
 - Move all GPIO API functions from generic.c into gpio.c
 - Convert all gpio functions into gpiolib callbacks.

Signed-off-by: Dmitry Baryshkov <dbaryshkov@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>