ARM: sunxi: select ARCH_REQUIRE_GPIOLIB

CONFIG_ARCH_SUNXI currently doesn't enable a gpiolib, which causes build
problems when building a kernel with only the sunxi platform enabled.
Select ARCH_REQUIRE_GPIOLIB to solve this.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Tested-by: Emilio López <emilio@elopez.com.ar>