ARM: dts: keystone: Add minimum support for K2G evm

Add barebones K2G evm dts. This DTS allows the board to boot using a
ram based filesystem.

The technical reference manual for K2G can be found here:
http://www.ti.com/lit/ug/spruhy8/spruhy8.pdf



Signed-off-by: Vitaly Andrianov <vitalya@ti.com>
Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>