sys: Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Allow kernel config to specify DTS/DTSO to build, and out-of-tree support

This allows for directives such as

makeoptions DTS+=/out/of/tree/myboard.dts
# in tree! Same rules applied as if this were in a dtb/ module
makeoptions DTS+=otherboard.dts

to be specified in config(5) and have these built/installed alongside th
kernel. The assumption that overlays live in an overlays/ directory is only
made for in-tree DTSO, but we still make the assumption that out-of-tree
arm64 DTS will be in vendored directories (for now).

This lowers the cost to hacking on an overlay or dts by being able to
quickly throw it in a custom config, especially if it doesn't fit one of the
current dtb/modules quite appropriately or it's not intended for commit
there.

The build/install targets were split out of dtb.mk to centralize the build
logic and leave out the all/realinstall/CLEANFILES additions... it was
believed that we didn't want to pollute the kernel build with these.

The build rules were converted to suffix rules at the suggestion of Ian to
clean things up a little bit in a world where we can have mixed
in-tree/out-of-tree DTS/DTSO specified.

Reviewed by: ian
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D19351

dtb.mk: Fix passing of ECHO to make_dtb{,o}.sh

Use ${ECHO} in dtb/dtbo build, pass in from dtb.mk for -s

Reported by: sbruno
MFC after: 3 days

dtb: aarch64 uses vendor subdirectories, handle that

Add dtb overlays support

DTB Overlays are useful to change/add nodes to a dtb without the need to
modify it.
Add support for building dtbo during buildkernel.
The goal of DTBO present in the FreeBSD source tree is to fill a gap in
time when we submit changes upstream (Linux). Instead of waiting 2 to 4 months
we can add a DTBO in tree in the meantime.
This is not for adding DTBO for capes/hat/addon boards, those will be
better to put in a ports.
This is also not for enabling a i2c/spi/pwm controller on certain pins,
each user have a different use case for those (which pins to use etc ...)
and we cannot have all possible configuration.

Add a dtbo for sun8i-h3-sid which add the SID node missing in upstream dts.

Reviewed by: kevans
Differential Revision: https://reviews.freebsd.org/D14782

Move sys/boot/fdt/dts to sys/dts and adjust scripts.

Sponsored by: Netflix

make.conf: Add the possibility to use another DTC

Add a make.conf DTC variable that control which DTC (Device Tree Compiler)
to use.

Reviewed by: bdrewery, imp
Differential Revision: https://reviews.freebsd.org/D9577

Honor LINKS=x y in dtb modules. We need this for compatibility links
for old, FreeBSD names.

Add missed updates for r301079 and r301084.

Do as r289391 did for share/mk and make installing to a non-existent directory
an error.

Most of these do a 'mkdir -p' or 'install -d' before installing, but add
the trailing / here for consistency with the userland install.

MFC after: 2 weeks
X-MFC-With: r289391
Sponsored by: EMC / Isilon Storage Division

Prefer install over mkdir to create the directory. Add test to ensure
the directory doesn't exist before creating it. This makes the NO_ROOT
case actually work.

Suggested by: brooks@

Move these definitions to bsd.own.mk along side the kernel directory /
user defines. Make this work with WITH_INSTALL_AS_USER as well.

Noticed by: ian@

Fix typo.

Submitted by: jhb@

We need to create /boot/dtb since some use cases don't create a full
root with BSD.root.mtree, so it often times will not exist. Rather
than force the latter for an installkernel, just create the directory
with a comment about why.

Submitted by: Guy Yur

Make sure that we define DTB{OWN,GRP,MODE} so install works.

Submitted by: Guy Yur

Add infrastructure to build dtb files from dts files.