Call for Testing: Switching back to our BSD licensed dtc(1)

dtc(1) is the Device Tree Compiler, used for embedded builds. We have
two versions of dtc(1) in the FreeBSD tree: a GPLv2 one from
https://git.kernel.org/cgit/utils/dtc/dtc.git and a BSD licensed one
in https://svn.freebsd.org/base/head/usr.bin/dtc.

We switched back to the GPL one since device tree files in the most
recent import required features not available in our own at the time.
However, as of r292876 the BSD licensed dtc(1) is functional and we
should be able to switch back to it.

I would encourage embedded users (primarily ARM boards) to test with
WITHOUT_GPL_DTC in /etc/src.conf and report their success or failure.

-Ed