arm64: allwinner: a64: Add A64-OLinuXino initial support

OLimex A64-OLinuXino is an open-source hardware board
using the Allwinner A64 SOC.

OLimex A64-OLinuXino has
- A64 Quad-core Cortex-A53 64bit
- 1GB or 2GB RAM DDR3L @ 672Mhz
- microSD slot and 4/8/16GB eMMC
- Debug TTL UART
- HDMI
- LCD
- IR receiver
- 5V DC power supply

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>