arm: dts: kirkwood: Enable upstream DT on Kirkwood boards

arm: dts: kirkwood: Enable upstream DT on Kirkwood boards

Enable OF_UPSTREAM to use upstream DT and add marvell/ prefix to the
DEFAULT_DEVICE_TREE for Kirkwood boards. And so we can directly build
DTBs from dts/upstream/src/arm/marvell, and including *-u-boot.dtsi
files from arch/arm/dts/ directory.

Background:

The following 2 commands and filters were used in the analysis to determine
which upstream DTS and DTSI files can be used as they are, or need to have
modified/created *-u-boot.dtsi for u-boot specific implementation, and
which board should be opt-out from OF_UPSTREAM.

"git grep -li arch_kirkwood configs | xargs grep DEVICE_TREE | cut -d '"' -f2 | xargs -n1 sh -c 'diff -qs  arch/arm/dts/$1.dts dts/upstream/src/arm/marvell/$1.dts' sh | grep differ"
"diff -qrbu arch/arm/dts/ dts/upstream/src/arm/marvell/ | grep kirkwood | grep ".dtsi ""

More detailed information can be found at:
https://lore.kernel.org/u-boot/20240328021825.17935-1-mibodhi@gmail.com/T/#u

I've regression tested this patch with the Zyxel NSA325 (Kirkwood 88F6282)
and Zyxel NSA310S (Kirkwood 88F6281). The Zyxel NSA325 board has a
USB 3.0 controller attached to the PCIe bus. And the Zyxel NSA310S
has an extensive overhaul in bindings and styles in upstream DTS version.

Tested-by: Michael Walle <michael@walle.cc> # on lschv2
Acked-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Tony Dinh <mibodhi@gmail.com>