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`
```

The RZN1 Snarc board does not seem to have a matching Linux kernel
DT counterpart, this is currently not switched to OF upstream.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>