ARM: dts: imx6ul-kontron-n6310: Add Kontron i.MX6UL N6310 SoM and boards

Add support for i.MX6UL modules from Kontron Electronics GmbH (before
acquisition: Exceet Electronics) and evalkit boards based on it:

1. N6310 SOM: i.MX6 UL System-on-Module, a 25x25 mm solderable module
   (LGA pads and pin castellations) with 256 MB RAM, 1 MB NOR-Flash,
   256 MB NAND and other interfaces,
2. N6310 S: evalkit, w/wo eMMC, without display,
3. N6310 S 43: evalkit with 4.3" display,

The work is based on Exceet/Kontron source code (GPLv2) with numerous
changes:
1. Reorganize files,
2. Rename Exceet -> Kontron,
3. Rename models/compatibles to match newest Kontron product naming,
4. Fix coding style errors and adjust to device tree coding guidelines,
5. Fix DTC warnings,
6. Extend compatibles so eval boards inherit the SoM compatible,
7. Use defines instead of GPIO and interrupt flag values,
8. Use proper vendor compatible for Macronix SPI NOR,
9. Replace deprecated bindings with proper ones,
10. Sort nodes alphabetically,
11. Remove Admatec display nodes (not yet supported).

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>