Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

various: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

Improvements to BSD-licensed DTC.

- Numerous crash and bug fixes
- Improved warning and error messages
- Permit multiple labels on nodes and properties
- Fix node@address references
- Add support for /delete-node/
- Consume whitespace after a node
- Read the next token before the second /memreserve/
- Fix parsing of whitespace
- Clean up /delete-node/ and add support for /delete-property/
- Handle /delete-node/ specifying a unit address

Obtained from: https://github.com/davidchisnall/dtc @df5ede4

Improvements to BSD-licensed DTC.

- Added an expression parser so that expressions from headers are now working
- Fixed missing null terminators on cross references
- Disabled exceptions / RTTI in the build for smaller binaries
- Changed phandle order generation to be identical to GPL'd dtc

Lots of improvements to the BSD-licensed dtc

- Various fixes to includes (including recursive includes)
- Lots of testing that the output exactly matches GPL'd dtc
- Lots of bug fixes to merging
- Fix incorrect mmap usage
- Ad-hoc memory management replaced with C++11 unique_ptr and similar

Patrick Wildt has successfully run many (all?) of the GPL dtc test suite.

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.