ARM: dts: mxs: Add MSR M28CU3 board

This board is based on the M28 SoM with custom baseboard. Supported
are LEDs, ethernet, PWM, LCD, SD slots.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>