arm64: dts: renesas: Add Renesas R8A779M2 SoC support

Add support for the Renesas R-Car M3e (R8A779M2) SoC, which is a
different grading of the R-Car M3-W+ (R8A77961) SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/2303577cac91aa6d98e7f2c72e36841f6218e53f.1628766192.git.geert+renesas@glider.be