ARM: dts: keystone-k2g: Add device state controller node

Add the device state controller node as a syscon node to the
K2G SoC. This module provides similar device control functionality
as that on the existing K2 SoCs.

One example usage would be the boot address programming of the
DSP processor sub-system.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>