Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add support for parameterised device tree sources to the device tree compiler.

Reviewed by: brooks
Sponsored by: DARPA, AFRL

Explicitly include headers that are implicitly included by libstdc++. Fixes
building dtc with libc++.

Fix logic error in explicitly specified dtb versions spotted by gavin.

Import new (BSDL) device tree compiler. Now built by default, so that it can't
be used on the host system (and not installed on the device, if required). The
GPL'd one is still available if there are any devices that need it (make
universe passes with it, including kernels that use fdt, but there may be some
out-of-tree ones). WITH_GPL_DTC can be used to select the old one, for now.

Probably won't be MFC'd, but we'll remove the GPL'd version in head after the
new one has had a lot more testing and ship it in 10.0.