ARM: dts: r8a77470: Initial SoC device tree

The initial R8A77470 SoC device tree including CPU0, GIC, timer, SYSC, RST,
CPG, and the required clock descriptions.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>