ARM: keystone: Enable PINCTRL_SINGLE Config

Newer Keystone 2 devices utilize pinmuxing. Enable PINCTRL SINGLE
which is used to handle pinmuxing.
Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>

arch/arm/configs/keystone_defconfig

@@ -144,6 +144,7 @@ CONFIG_I2C_DAVINCI=y
 CONFIG_SPI=y
 CONFIG_SPI_DAVINCI=y
 CONFIG_SPI_SPIDEV=y
+CONFIG_PINCTRL_SINGLE=y
 CONFIG_GPIOLIB=y
 CONFIG_GPIO_SYSFS=y
 CONFIG_GPIO_DAVINCI=y