usbgadget: autostart: add DFU support ...

Use global variable dfu_function to autostart DFU. As similar code
is used to start multifunction gadget using command, move common
code to common/usbgadget.c and consolidate it.
It turned out that '-s' option of usbgadget command does nothing,
so remove its help text and make it function as '-a'.

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

usb: gadget: properly release f_multi_opts ...

The usbgadget commands uses statically allocated f_multi_opts and passes
this to usb_multi_register(). These f_multi_opts are of course no
longer valid when we leave the usbgadget command. Luckily we do not use
the data after we left the usbgadget command, so this never has been a
problem. However, f_multi_opts has some allocated members which we can
not free anymore on gadget unregistration because we no longer have the
pointer to them.

Fix this by adding a release function to struct f_multi_opts. This way
we can allocate all memory dynamically and properly free it when not
used anymore.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

USB: gadget: Add a multi function gadget ...

Similar to the Kernel multi function this gadget driver is used
for creating a USB device with multiple functions. This is
created and removed with the newly created 'usbgadget' command.
Based on the options it creates combinations of DFU, fastboot
and serial USB functions.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>