usbtty: adapt buffers for large packet support

Increase buffer sizes at driver and tty level to accommodate kermit
large packet support.

Signed-off-by: Shiraz Hashim <shiraz.hashim@st.com>
diff --git a/include/usbdevice.h b/include/usbdevice.h
index 3edaf8b..7037efd 100644
--- a/include/usbdevice.h
+++ b/include/usbdevice.h
@@ -475,7 +475,9 @@
  * function driver to inform it that data has arrived.
  */
 
-#define URB_BUF_SIZE 128 /* in linux we'd malloc this, but in u-boot we prefer static data */
+/* in linux we'd malloc this, but in u-boot we prefer static data */
+#define URB_BUF_SIZE 512
+
 struct urb {
 
 	struct usb_endpoint_instance *endpoint;