ARM: dts: imx6ul: Add DTS for liteSOM module

This is a SOM (System on Module), so it will be part of another boards.
Hence, this is a "dtsi" file that will be included from another device
tree files.

Hardware specification:
 * Freescale i.MX6UL SoC
 * up to 512 MB RAM
 * eMMC on uSDHC2

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>