ARM: dts: uniphier: Add support for Akebi96

Add the device tree for Akebi96. Akebi96 is a 96boards certified
development board based on UniPhier LD20.
( https://www.96boards.org/product/akebi96/

 )

Signed-off-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>