Add the initial device  tree for  the R8A77970 SoC based Eagle board.
The board has 1 debug serial port (SCIF0); include support for it,
so that the serial console can work.

Based on the original (and large) patch by Vladimir Barinov
<vladimir.barinov@cogentembedded.com>.
Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>