usb: dwc3: add a SPL_USB_DWC3_GENERIC option for the dwc3 driver

Suppress warnings when building the SPL without USB_DWC3_GENERIC

Signed-off-by: Angus Ainslie <angus@akkea.ca>
diff --git a/drivers/usb/dwc3/Kconfig b/drivers/usb/dwc3/Kconfig
index 62aa65b..f010291 100644
--- a/drivers/usb/dwc3/Kconfig
+++ b/drivers/usb/dwc3/Kconfig
@@ -30,6 +30,13 @@
 	  Select this for Xilinx ZynqMP and similar Platforms.
 	  This wrapper supports Host and Peripheral operation modes.
 
+config SPL_USB_DWC3_GENERIC
+	bool "Generic implementation of a DWC3 wrapper (aka dwc3 glue) for the SPL"
+	depends on SPL_DM_USB && USB_DWC3 && SPL_MISC
+	help
+	  Select this for Xilinx ZynqMP and similar Platforms.
+	  This wrapper supports Host and Peripheral operation modes.
+
 config USB_DWC3_MESON_G12A
 	bool "Amlogic Meson G12A USB wrapper"
 	depends on DM_USB && USB_DWC3 && ARCH_MESON