usb: dwc3: Move CONFIG_USB_DWC3_GADGET/HOST to Kconfig

Description was borrowed from kernel dwc3 Kconfig.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
diff --git a/configs/odroid-xu3_defconfig b/configs/odroid-xu3_defconfig
index da92b2d..cb6035b 100644
--- a/configs/odroid-xu3_defconfig
+++ b/configs/odroid-xu3_defconfig
@@ -20,6 +20,7 @@
 CONFIG_USB=y
 CONFIG_DM_USB=y
 CONFIG_USB_DWC3=y
+CONFIG_USB_DWC3_GADGET=y
 CONFIG_USB_GADGET=y
 CONFIG_USB_GADGET_DOWNLOAD=y
 CONFIG_VIDEO_BRIDGE=y