ARM: dts: imx6: Add support for Phytec phyBOARD i.MX6UL Segin

The Phytec phyBOARD Segin is i.MX6 based SBC, available with either an
i.MX6UL or i.MX6ULL SOM and various add-on boards.

The following adds support for the "Full Featured" version of the Segin,
which is provided with the i.MX6UL SOM and the PEB-EVAL-01 evaluation
module.

Its hardware specifications are:

 * 512MB DDR3 memory
 * 512MB NAND flash
 * 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

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>