arm64: dts: renesas: Add Renesas R8A779M6 SoC support

Add support for the Renesas R-Car E3e (R8A779M6) SoC, which is a
different grading of the R-Car E3 (R8A77990) SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/004e837531de4160ac4815fe7836b1f05d6fad85.1628766192.git.geert+renesas@glider.be