include: also check CONFIG_GPIOLIB for GPIO_SUPPORT

Recent kernels removed GENERIC_GPIO and require GPIO capable
targets to select GPIOLIB instead, so check for both symbols.

Fixed #13814.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt@37166 3c298f89-4303-0410-b956-a3cf2f4a3e73