arm64: dts: renesas: Add support for Salvator-XS with R-Car M3e-2G

Add support for the Renesas Salvator-X 2nd version development
board equipped with an R-Car M3e-2G SiP.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/177666b6ffa0b404e1e45504763dd381107a02f3.1626708063.git.geert+renesas@glider.be