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/usb/gadget/Makefile b/drivers/usb/gadget/Makefile
index 5b18e8c..0fbbb7c 100644
--- a/drivers/usb/gadget/Makefile
+++ b/drivers/usb/gadget/Makefile
@@ -9,6 +9,7 @@
 obj-$(CONFIG_USB_ETHER) += epautoconf.o config.o usbstring.o
 
 ifdef CONFIG_SPL_BUILD
+obj-$(CONFIG_SPL_USB_GADGET_SUPPORT) += g_dnl.o
 obj-$(CONFIG_SPL_DFU_SUPPORT) += f_dfu.o
 endif
 
@@ -21,8 +22,8 @@
 obj-$(CONFIG_USB_GADGET_DWC2_OTG_PHY) += dwc2_udc_otg_phy.o
 obj-$(CONFIG_USB_GADGET_FOTG210) += fotg210.o
 obj-$(CONFIG_CI_UDC)	+= ci_udc.o
-obj-$(CONFIG_USB_GADGET_DOWNLOAD) += g_dnl.o
 ifndef CONFIG_SPL_BUILD
+obj-$(CONFIG_USB_GADGET_DOWNLOAD) += g_dnl.o
 obj-$(CONFIG_USB_FUNCTION_THOR) += f_thor.o
 obj-$(CONFIG_USB_FUNCTION_DFU) += f_dfu.o
 obj-$(CONFIG_USB_FUNCTION_MASS_STORAGE) += f_mass_storage.o