gadget-cli: composable ConfigFS usage #2
Description
Currently we just stomp on any existing gadget configured in ConfigFS, and set up our own.
We should continue to support this mode to make it maximally easy to start up smoo and kick the tires. But it should not be the default. Instead, the default behaviour of smoo-gadget-cli should be to require a --ffs-dir=/sys/kernel/config/usb/usb_gadget/foo/functions/smoo.ffs flag. This way, the gadget can be trivially composed with a more featureful gadget configuration. This also paves the way for distro adoption.