ARM: dts: imx6dl: Add support for Sielaff i.MX6 Solo board

The Sielaff i.MX6 Solo board is used as controller and user interface
in vending machines. It is based on the i.MX6 Solo SoC and features
the following peripherals and interfaces:

* 512 MB DDR3 RAM
* 512 MB NAND Flash
* 1 MB NOR Flash
* SD card
* Debug LED
* Debug UART
* Key Inputs
* RTC
* RS232
* 100 MBit Ethernet
* USB Hub
* USB OTG
* HDMI
* 7" LVDS IPS panel
* PWM Backlight
* Optional Extension Board with USB Ethernet NIC

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>