Doc: ABI: configfs-usb-gadget-sourcesink: add two entries for depth of queue

Add both bulk and iso depth of queue entries.
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

Documentation/ABI/testing/configfs-usb-gadget-sourcesink

@@ -10,3 +10,5 @@ Description:
 		isoc_mult	- 0..2 (hs/ss only)
 		isoc_maxburst	- 0..15 (ss only)
 		buflen		- buffer length
+		bulk_qlen	- depth of queue for bulk
+		iso_qlen	- depth of queue for iso