ARM: dts: r8a7744: Initial SoC device tree

Basic support for the RZ/G1N (R8A7744) SoC. Added placeholders
to avoid compilation error with the common platform code.

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