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

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

Fix test-dts{,o} targets

There were two main problems here:

1.) sys/dts/Makefile.inc is not included from various */overlays directories
by default, only ../Makefile.inc
2.) When shelling out for DTS/DTSO, cwd != .CURDIR, so enumeration always
failed

These changes allow make test-dts and make test-dtso to function in their
respective directories.

Reviewed by: manu
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D17961

arm64: Add DTS overlays for A64

- sun50i-a64-sid.dtso registers the Security ID node, needed for thermal
- sun50i-a64-ths.dtso registers the thermal node, for which we already have a
driver
- sun50i-a64-timer.dtso registers the timer node, needed as the generic timer
glitch on A64 SoC.

Approved by: re (gjb)

dts: arm64: allwinner: Remove unused dts for pine64

Latest u-boot port provide the dts for pine64, remove our custom
and outdated dts for this board.

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

Sponsored by: Netflix