usb: gadget: cdc2: convert to new interface of f_ecm

f_ecm has been converted to new configfs infrastructure,
fixing cdc2 gadget driver.

[ balbi@ti.com : fixed a bunch of errors when adding ECM function ]

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
index 6f1afd7..fcc3bfb 100644
--- a/drivers/usb/gadget/Kconfig
+++ b/drivers/usb/gadget/Kconfig
@@ -838,6 +838,7 @@
 	select USB_U_SERIAL
 	select USB_U_ETHER
 	select USB_F_ACM
+	select USB_F_ECM
 	help
 	  This driver provides two functions in one configuration:
 	  a CDC Ethernet (ECM) link, and a CDC ACM (serial port) link.