staging: usb: gadget: Add Configurable Composite Gadget driver

The Configurable Gadget driver is a composite driver that allows
userspace to change at runtime the list of functions enabled in
its configuration and to configure these functions. It supports
multiple functions: acm, rndis, and mass storage.

It is usually controlled by a daemon that changes the configuration
based on user settings. For example, rndis is enabled when the user
enables sharing the phone data connection.

As an example on how to use it, the following shell commands will
make the gadget disconnect from the host and make it be re-enumerated
as a composite with 1 rndis and 2 acm interfaces, and a different
product id:

echo 0       > /sys/class/ccg_usb/ccg0/enable
echo rndis,acm > /sys/class/ccg_usb/ccg0/functions
echo 2       > /sys/class/ccg_usb/ccg0/f_acm/instances
echo -n 0x2d01 > /sys/module/g_ccg/parameters/idProduct
echo 1       > /sys/class/ccg_usb/ccg0/enable

The driver requires a gadget controller that supports software
control of the D+ pullup and the controller driver must support
disabling the pullup during composite_bind.

Signed-off-by: Mike Lockwood <lockwood@android.com>
Signed-off-by: Benoit Goby <benoit@android.com>
	[import from android.c, implement review comments, remove adb,mtp,ptp,accessory]
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>