ARM: dts: imx6ull: Add support for PHYTEC phyBOARD-Segin with i.MX 6ULL

In addition to the PHYTEC phyCORE-i.MX 6UL the PHYTEC phyBOARD-Segin is
also available with the PHYTEC phyCORE-i.MX 6ULL. So this adds support
for this SOM and its baseboards.

It comes in a full featured option with either NAND flash or eMMC and in
a low cost option only available with NAND flash.

The hardware specs are:

 - Full featured with NAND or eMMC:
    * i.MX 6ULL Y2
    * 512MB DDR3 memory
    * 512MB NAND flash or 4GB/8GB eMMC
    * Dual 10/100 Ethernet
    * USB Host and USB OTG
    * RS232
    * MicroSD external storage
    * Audio, RS232, I2C, SPI, CAN headers
    * Further I/O options via A/V and Expansion headers

 - Low cost with NAND:
    * i.MX 6ULL Y0
    * 256MB DDR3 memory
    * 128MB NAND flash
    * Single 10/100 Ethernet
    * USB OTG
    * RS232
    * MicroSD external storage
    * I2C
    * Further I/O options via Expansion headers

Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>