usb: dwc3: core: add flag for EP0 direction

Add a flag to keep track of ep0 direction.
This flag will be used on a following patch.

Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/core.h

@@ -350,6 +350,9 @@ struct dwc3_ep {
 #define DWC3_EP_PENDING_REQUEST	(1 << 5)
 #define DWC3_EP_WILL_SHUTDOWN	(1 << 6)
 
+	/* This last one is specific to EP0 */
+#define DWC3_EP0_DIR_IN		(1 << 31)
+
 	unsigned		current_trb;
 
 	u8			number;