ARM: dts: renesas: Switch to using upstream DT on 64bit Renesas SoCs

Enable OF_UPSTREAM to use upstream DT and add renesas/ prefix to the
DEFAULT_DEVICE_TREE and OF_LIST. And thereby directly build DTB from
dts/upstream/src/ including *-u-boot.dtsi files from arch/$(ARCH)/dts/
directory.

The configuration update has been done using the following script:
```
sed -i '/^CONFIG_DEFAULT_DEVICE_TREE/ s@="@&renesas/@' `git grep -li renesas configs`
sed -i '/^CONFIG_OF_LIST/ s@r8a@renesas/&@g' `git grep -li renesas configs`
```

There are SoCs which are not included in this patch. The 32bit SoCs
require further infrastructure work. R8A779H0 is coming during the
next upstream DT synchronization cycle as it is not included in
current upstream DTs yet.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by:  Adam Ford <aford173@gmail.com> # Beacon boards
Reviewed-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>