arm64: defconfig: Enable R8A779A0 SoC

Enable the Renesas R-Car V3U (R8A779A0) SoC in the ARM64 defconfig.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20201109115540.2415328-1-geert+renesas@glider.be