MFC r315009:

Merge from vendor branch importing dtc 1.4.3

Major new feature in this import is FDT overlay support

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Merge from vendor branch importing dtc git rev 6a15eb2350426d285130e4c9d84c0bdb6575547a

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.

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)

Update DTC to git d75b33af676d0beac8398651a7f09037555a550b.

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

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

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