ARM: configs: libretech-ac: enable USB_DFU like in meson64.h

USB_DFU was added in meson64.h but is missing in libretech-ac.h,
fix this to enable DFU RAM boot for libretech-ac.

Fixes 4aa027b3f8 ("configs: meson64: add alternate USB DFU boot target")

Link: https://lore.kernel.org/r/20231102-libretech-ac-fix-dfu-v1-1-112379165028@linaro.org
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
diff --git a/include/configs/libretech-ac.h b/include/configs/libretech-ac.h
index bf20d31..16239f2 100644
--- a/include/configs/libretech-ac.h
+++ b/include/configs/libretech-ac.h
@@ -11,6 +11,7 @@
 
 #define BOOT_TARGET_DEVICES(func) \
 	func(ROMUSB, romusb, na)  \
+	func(USB_DFU, usbdfu, na)  \
 	func(MMC, mmc, 0) \
 	BOOT_TARGET_DEVICES_USB(func) \
 	func(PXE, pxe, na) \