ARM: dts: imx6ull: add MYiR MYS-6ULX SBC

Add support for the MYiR imx6ULL based single board computer
equipped with on board 256MB NAND & RAM. The board also
provides expansion header for expansion board, but this
commit adds only support for SBC.

Signed-off-by: Parthiban Nallathambi <parthiban@linumiz.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>