serial: sh-sci: Add device tree bindings documentation

Document the device tree bindings for the sci serial port devices.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

diff --cc Documentation/devicetree/bindings/serial/renesas,sci-serial.txt
Simple merge