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

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

Update to latest git version of dtc to get new dtsv2 support,
including the include directive.

Fix minor build issue corrected by converting yypush_buffer_state and
yypop_buffer_state to yy_set_buffer_state and a hard-coded 100-deep
stack. It was easier to fix it here than to import that support into
our flex.

The new tools and test hardness remain unsupported at the moment.

Provide kernel level headers for the libfdt code.

Reviewed by: imp
Sponsored by: The FreeBSD Foundation

Merge DTC-d75b33af.

This is a split merge because of non-uniform licensing of the DTC package
contents and the way these components will be used in the FreeBSD environment.

The original DTC package is composed of the following two major pieces:

1. sys/contrib/libfdt (BSD [dual] license)
2. contrib/dtc (GPLv2)

The libfdt component is going to be shared in all aspects of the environment:
- /boot/loader
- kernel
- dtc (the device tree compiler proper, userspace tool)

Initial import of the Device Tree Compiler (DTC) package v1.2.0.

Obtained from: git://git.jdl.com/software/dtc.git