[AppStream] Selecting a "driver" to be used using an AppStream file

[Richard Hughes]

In fwupd we support several "providers" which are used to update
firmware on different device types. Some devices have vendor specific
quirks, and it would be really handy to put that information in the
appstream file itself rather than having to add another VID:PID to the
fwupd binary and recompiling for all distros in all supported
releases.

At the moment I'm using the dreaded <metadata> tag in my prototype and
defining something like: <value key="VendorDriver">Dfu0110</value> --
but there must be a better way to do this. <provides> seems like the
wrong way; I almost want a <requires> but that has too many bad
connotations. Ideas?

Richard