usb gadget serial: split out CDC ACM function

Split out CDC ACM parts of "gadget serial" to a "function driver".
Some key structural differences from the previous ACM support, shared
with with the generic serial function (next patch):

 - As a function driver, it can be combined with other functions.
   One gadget configuration could offer both serial and network
   links, as an example.

 - One serial port can be exposed in multiple configurations;
   the /dev/ttyGS0 node could be exposed regardless of which
   config the host selected.

 - One configuration can expose multiple serial ports, such as
   ttyGS0, ttyGS1, ttyGS2, and ttyGS3.

This code should be a lot easier to understand than the previous
all-in-one-big-file version of the driver.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/DocBook/gadget.tmpl

@@ -556,6 +556,8 @@ been converted to this framework.
 Near-term plans include converting all of them, except for "gadgetfs".
 </para>
 
+!Edrivers/usb/gadget/f_acm.c
+
 </sect1>
 
 

drivers/usb/gadget/Makefile

@@ -26,7 +26,7 @@ C_UTILS =	composite.o usbstring.o config.o epautoconf.o
 
 g_zero-objs			:= zero.o f_sourcesink.o f_loopback.o $(C_UTILS)
 g_ether-objs			:= ether.o usbstring.o config.o epautoconf.o
-g_serial-objs			:= serial.o u_serial.o usbstring.o config.o epautoconf.o
+g_serial-objs			:= serial.o u_serial.o f_acm.o $(C_UTILS)
 g_midi-objs			:= gmidi.o usbstring.o config.o epautoconf.o
 gadgetfs-objs			:= inode.o
 g_file_storage-objs		:= file_storage.o usbstring.o config.o \