arm64: dts: renesas: Add support for M3ULCB with R-Car M3-W+

Add initial support for the Renesas M3ULCB board equipped with an R-Car
M3-W+ SiP with 8 (2 x 4) GiB of RAM.
To avoid build error on 'ulcb.dtsi', ssi2 is added into 'r8a77961.dtsi'.

Based on commit 92980759 ("arm64: dts: renesas: Add support for
Salvator-XS with R-Car M3-W+").

Signed-off-by: Yuya Hamamachi <yuya.hamamachi.sx@renesas.com>
Link: https://lore.kernel.org/r/20200309064425.25437-3-yuya.hamamachi.sx@renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>