ARM: dts: sun7i: Add dts file for pcDuino 3 Nano board

Add support for the LinkSprite pcDuino 3 Nano board. This is a low-cost
Allwinner A20 board with Arduino-style GPIO headers; it features 1G RAM,
4G NAND flash, 1 micro-SD, 2 USB sockets, 1 micro USB socket for OTG and
another for power in, HDMI, SATA, 5V power for SATA devices, gigabit
Ethernet, an IR receiver, 3.5mm audio out and a MIPI camera connector.

For more details, see: http://linux-sunxi.org/LinkSprite_pcDuino3_Nano



Changes in v3:
- rename LEDs to pcduino3-nano:green:usr[12]
- remove optional features on Arduino headers (i2c2, spi0, uart2)

Signed-off-by: Adam Sampson <ats@offog.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>