usb: introduce a separate config option for DM USB device

Using CONFIG_DM_USB for this purpose prevents using DM_USB for host and not
for device.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
diff --git a/drivers/usb/dwc3/dwc3-generic.c b/drivers/usb/dwc3/dwc3-generic.c
index 56c9fd6..ad3a116 100644
--- a/drivers/usb/dwc3/dwc3-generic.c
+++ b/drivers/usb/dwc3/dwc3-generic.c
@@ -21,8 +21,7 @@
 #include "gadget.h"
 #include "linux-compat.h"
 
-DECLARE_GLOBAL_DATA_PTR;
-
+#if CONFIG_IS_ENABLED(DM_USB_GADGET)
 int usb_gadget_handle_interrupts(int index)
 {
 	struct dwc3 *priv;
@@ -97,6 +96,7 @@
 	.priv_auto_alloc_size = sizeof(struct dwc3),
 	.flags	= DM_FLAG_ALLOC_PRIV_DMA,
 };
+#endif
 
 static int dwc3_generic_bind(struct udevice *parent)
 {