ARM: shmobile: henninger: initial device tree

Add the initial device tree for the R8A7791 SoC based Henninger board. SCIF0
serial port support is included, so that the serial console can work.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>