ARM: dts: blanche: initial device tree

Add the initial device  tree for the R8A7792 SoC based Blanche board.
The board has 2 debug serial ports: SCIF0 and SCIF3; include support for
them,  so that  the serial console  can  work.

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>