arm: sun7i: Add sun7i-a20-icnova-swac.dts

This baseboard from SWAC is equipped with the ICnova-A20 SoM from
Incircuit. This board is equipped with the following interfaces /
devices:

- 512 MiB SDRAM
- 4 GiB MLC NAND (Micron MT29F32G08CBACAWP or Hynix H27UBG8T2BTR)
- USB host
- LCD 800x480
- HDMI
- CAN

Note that the NAND support is still missing. As its currently not
supported in mainline for sunxi and especially for these MLC
devices.

The original plan was to also provide a dtsi for the ICnova SoM,
to put all the SoM internal nodes / properties there. But as I
don't have a clear overview of the SoM specific and baseboard
specific differences, I'm putting all in one dts for now. Once
somebody pushed support for some other baseboard using the
A20 SoM from Incircuit (e.g. the ADB4006 reference design), this
should be separated.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Marcus Heuer <marcus.heuer@swac.de>
[maxime: Fixed CPU regulator upper voltage boundary]
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>