Match unattached devices on the system to potential kernel modules.

devmatch(8) matchs up devices in the system device tree with drivers
that may match them. For each unattached device in the system, it
tries to find matching PNP info in the linker hints and prints modules
to load to claim the devices.

In --unbound mode, devmatch can look for drivers that have attached to
devices in the device tree and have plug and play information, but for
which no PNP info exists. This helps find drivers that haven't been
converted yet that are in use on this system.

In addition, the ability to dump out linker.hints is provided.

Future commits will add hooks to devd.conf and rc.d to fully automate
using this information.