When trying to match the nomatch event passed to us, attempt to look
up the device described by the nomatch event in the device tree. If we
find it, then if the device is marked as have already attached to a
device once, then ignore the device.

This keeps us from reloading the device driver when it has just been
manually unloaded. All devies that have had a driver attach to them at
least once no longer participate in pnp-based autoloading.

Differential Revision: https://reviews.freebsd.org/D16735