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

Converting f_phonet to the new function interface requires converting
the f_phonet's function code and its users.

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

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

The old function interface is provided by means of 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/Makefile b/drivers/usb/gadget/Makefile
index 66152f5..db8ce05 100644
--- a/drivers/usb/gadget/Makefile
+++ b/drivers/usb/gadget/Makefile
@@ -52,6 +52,8 @@
 obj-$(CONFIG_USB_F_NCM)		+= usb_f_ncm.o
 usb_f_ecm-y			:= f_ecm.o
 obj-$(CONFIG_USB_F_ECM)		+= usb_f_ecm.o
+usb_f_phonet-y			:= f_phonet.o
+obj-$(CONFIG_USB_F_PHONET)	+= usb_f_phonet.o
 
 #
 # USB gadget drivers