usb: gadget: f_rndis: convert to new function interface with backward compatibility

Converting rndis to the new function interface requires converting
the USB rndis' function code and its users.

This patch converts the f_rndis.c to the new function interface.

The file is now compiled into a separate usb_f_rndis.ko module.

The old function interface is provided by means of a preprocessor
conditional directives. After all users are converted, the old interface
can be removed.

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/g_ffs.c b/drivers/usb/gadget/g_ffs.c
index 3d290e5..5327c82 100644
--- a/drivers/usb/gadget/g_ffs.c
+++ b/drivers/usb/gadget/g_ffs.c
@@ -33,6 +33,7 @@
 #define USB_FSUBSET_INCLUDED
 #  include "f_subset.c"
 #  ifdef USB_ETH_RNDIS
+#    define USB_FRNDIS_INCLUDED
 #    include "f_rndis.c"
 #    include "rndis.h"
 #  endif