sunxi: Add 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.

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.

This patch adds defconfig and dts files for this board. The dts is same
with mainline kernel, except some nodes are removed to make file
compatible with existing dtsi file.

Signed-off-by: Stefan Mavrodiev <stefan@olimex.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>