[nrf fromtree] dts: nordic: nrf54h20: define global power domain

Add the global power domain entry. This domain is not memory-mapped
but controlled using NRFS services.

Signed-off-by: Gerard Marull-Paretas <[email protected]>
(cherry picked from commit a56a170)

Author: gmarull

dts/common/nordic/nrf54h20.dtsi

@@ -197,6 +197,11 @@
 		};
 	};
 
+	gpd: global-power-domain {
+		compatible = "nordic,nrf-gpd";
+		#power-domain-cells = <1>;
+	};
+
 	soc {
 		#address-cells = <1>;
 		#size-cells = <1>;