ARM: sunxi: Increase the number of GPIOs available

The Allwinner A10 has 9 banks of 32 GPIOs available, so it doesn't fit
in the usual 256 limit set by gpio.h. Increase this number to 288.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>