usb: gadget: f_tcm: convert to new function interface with backward c…

…ompatibility

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

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

The file can be now compiled into a separate module usb_f_tcm.ko.

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>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/usb/gadget/Kconfig

@@ -199,6 +199,9 @@ config USB_F_HID
 config USB_F_PRINTER
 	tristate
 
+config USB_F_TCM
+	tristate
+
 choice
 	tristate "USB Gadget Drivers"
 	default USB_ETH

drivers/usb/gadget/function/Makefile

@@ -44,3 +44,5 @@ usb_f_hid-y			:= f_hid.o
 obj-$(CONFIG_USB_F_HID)		+= usb_f_hid.o
 usb_f_printer-y			:= f_printer.o
 obj-$(CONFIG_USB_F_PRINTER)	+= usb_f_printer.o
+usb_f_tcm-y			:= f_tcm.o
+obj-$(CONFIG_USB_F_TCM)		+= usb_f_tcm.o