arm64: dts: renesas: Add CPU topology on R-Car Gen3 SoCs

This patch adds the "cpu-map" into r8a7795/r8a7796 composed of
multi-cluster. This definition is used to parse the cpu topology.

Signed-off-by: Gaku Inami <gaku.inami.xh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>