Add the initial device tree for the R8A7792  SoC based Wheat board.
The Wheat board itself has  no serial ports  wired up, the USB serial chips
are situated on a separate  debug board and  one of them is connected to
SCFI0  -- include unconditional 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: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>