usb: core: skip interfaces disabled in devicetree

If an interface has an associated devicetree node with status disabled,
do not register the device.  This is useful for boards with a built-in
multifunction USB device where some functions are broken or otherwise
undesired.

Signed-off-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>