usb: dwc3-generic: Disable host driver definition if gadget only

Even if only USB gadget is defined, dwc3 generic driver enables
a definition and probe/remove functions for host driver.

This enables the definition if USB_HOST is enabled only.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
diff --git a/drivers/usb/dwc3/dwc3-generic.c b/drivers/usb/dwc3/dwc3-generic.c
index 30f835e..c8bf4ae 100644
--- a/drivers/usb/dwc3/dwc3-generic.c
+++ b/drivers/usb/dwc3/dwc3-generic.c
@@ -163,7 +163,8 @@
 };
 #endif
 
-#if defined(CONFIG_SPL_USB_HOST_SUPPORT) || !defined(CONFIG_SPL_BUILD)
+#if defined(CONFIG_SPL_USB_HOST_SUPPORT) || \
+	!defined(CONFIG_SPL_BUILD) && defined(CONFIG_USB_HOST)
 static int dwc3_generic_host_probe(struct udevice *dev)
 {
 	struct xhci_hcor *hcor;