usb: gadget: imx_udc: make it depend on BROKEN

that driver hasn't been maintained for quite
some time, at least since e08300043e (ARM:
imx: dynamically allocate imx_udc device).

Because of that, and because driver doesn't
even compile with allyesconfig and allmodconfig,
we're making it depend on BROKEN.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>