ARM: dts: k2g: Add device state controller node

Add the device state controller node as a syscon node to the
Keystone 2 Galileo 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>
[s-anna@ti.com: relocate node and revise commit description]
Signed-off-by: Suman Anna <s-anna@ti.com>