ARM: exynos_defconfig: enable USB gadget support

Enable USB gadget support without support for any specific gadgets to
more easily catch cases where a devices dts doesn't specify the usb
controllers dr_mode while it should.

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

arch/arm/configs/exynos_defconfig

@@ -55,6 +55,7 @@ CONFIG_SMSC911X=y
 CONFIG_USB_USBNET=y
 CONFIG_USB_NET_SMSC75XX=y
 CONFIG_USB_NET_SMSC95XX=y
+CONFIG_USB_GADGET=y
 CONFIG_INPUT_EVDEV=y
 CONFIG_KEYBOARD_GPIO=y
 CONFIG_KEYBOARD_CROS_EC=y