ARM: config: keystone: enable gpio support

Enable enable GPIO support for Keystone by setting CONFIG_GPIOLIB and
CONFIG_GPIO_DAVINCI options in keystone_defconfig.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>