spl: add USB Gadget config option

Introduce USB Gadget config option. This allows to combine Makefile
entries for SPL_USBETH_SUPPORT and SPL_DFU_SUPPORT.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Acked-by: Lukasz Majewski <l.majewski@samsung.com>
Tested-by: Ravi Babu <ravibabu@ti.com>
diff --git a/drivers/Makefile b/drivers/Makefile
index 40aba58..c19fa14 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -33,9 +33,8 @@
 obj-$(CONFIG_SPL_ETH_SUPPORT) += net/phy/
 obj-$(CONFIG_SPL_USBETH_SUPPORT) += net/phy/
 obj-$(CONFIG_SPL_MUSB_NEW_SUPPORT) += usb/musb-new/
-obj-$(CONFIG_SPL_USBETH_SUPPORT) += usb/gadget/
-obj-$(CONFIG_SPL_DFU_SUPPORT) += usb/gadget/
-obj-$(CONFIG_SPL_DFU_SUPPORT) += usb/gadget/udc/
+obj-$(CONFIG_SPL_USB_GADGET_SUPPORT) += usb/gadget/
+obj-$(CONFIG_SPL_USB_GADGET_SUPPORT) += usb/gadget/udc/
 obj-$(CONFIG_SPL_DFU_SUPPORT) += dfu/
 obj-$(CONFIG_SPL_WATCHDOG_SUPPORT) += watchdog/
 obj-$(CONFIG_SPL_USB_HOST_SUPPORT) += usb/host/