ARM: 8281/1: sa1100: move GPIO-related IRQ code to gpio driver

As a part of driver consolidation, move GPIO-related IRQ code to
drivers/gpio/gpio-sa1100.c. The code does not use GPIOLIB_IRQCHIP (yet),
because sa1100 does not have a device for gpios, which is a requirement
for GPIOLIB_IRQCHIP. This will be the next step.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>