Add initial DTSI for RZ/G2UL SoC.

Both RZ/G2L and RZ/G2UL uses the same SMARC EVK. Therefore they share
the common dtsi (rz-smarc.dtsi) file. Place holders are added in
device nodes to avoid compilation errors for the devices which have
not been enabled yet on RZ/G2UL SoC.
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20220412161314.13800-3-biju.das.jz@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>