ARM: dts: sk-rzg1m: initial device tree

Add the initial device  tree for the R8A7743 SoC based SK-RZG1M board.
The board has one debug serial port (SCIF0); include support for it, so
that  the serial  console  can work.

Based on the original (and large) patch by Dmitry Shifrin
<dmitry.shifrin@cogentembedded.com>.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>