arm64: dts: uniphier: Add support for Akebi96

arm64: dts: uniphier: Add support for Akebi96

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

This board has;
- MAX3421 USB-SPI chip on SPI port3 (for USB gadget port)
- Simple frame buffer with 1080p fixed resolution.
- I2S port which is connected to aout1b instead of aout1.
- 3 serial ports, only serial3 has CTS/RTS.
- No NAND, only eMMC on the board.
- OP-TEE installed firmware.

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