ARM: dts: sunxi: Add Olimex A20-SOM204-EVB board

ARM: dts: sunxi: Add Olimex A20-SOM204-EVB board

This is new System-On-Module platform with universal dimm socket for
easy insertation. The EVB board is designed to be universal with
future modules. Product page is located here [1].

There are two dts files - one for base model and another for eMMC variant.

Base features of A20-SOM204 board includes:
	* 1GB DDR3 RAM
	* AXP209 PMU
	* KSZ9031 Gigabit PHY
	* AT24C16 EEPROM
	* Status LED
	* LCD connector
	* GPIO connector

There will be variants with the following options:
	* Second LAN8710A Megabit PHY
	* 16MB SPI Flash memory
	* eMMC card
	* ATECC508 crypto device

The EVB board has:
	* Debug UART
	* MicroSD card connector
	* USB-OTG connector
	* Two USB host
	* RTL8723BS WiFi/BT combo
	* IrDA transceiver/receiver
	* HDMI connector
	* VGA connector
	* Megabit ethernet transceiver
	* Gigabit ethernet transceiver
	* SATA connector
	* CAN driver
	* CSI camera
	* MIC and HP connectors
	* PCIe x4 connector
	* USB3 connector
	* Two UEXT connectors
	* Two user LEDs

Some of the features are multiplexed and cannot be used the same time:
CAN and Megabit PHY. Others are not usable with A20 SoC: PCIe and USB3.

[1] https://www.olimex.com/Products/SOM204/

Signed-off-by: Stefan Mavrodiev <stefan@olimex.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>