ARM: 8279/1: sa1100: merge both GPIO irqdomains

Now there is no difference between low and high GPIO irqdomains. Merge
them into single irqdomain handling all GPIOs.

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>