arm64: dts: allwinner: h6: Introduce Tanix TX6 board

Tanix TX6 is an Allwinner H6 based TV box, which supports:
- Allwinner H6 Quad-core 64-bit ARM Cortex-A53
- GPU Mali-T720
- 4GiB DDR3 RAM (3GiB useable)
- 100Mbps EMAC via AC200 EPHY
- Cdtech 47822BS Wifi/BT
- 2x USB 2.0 Host and 1x USB 3.0 Host
- HDMI port
- IR receiver
- 64GiB eMMC
- 5V/2A DC power supply

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>