[nrf fromlist] boards: nordic: nrf54h20dk iron board radiocore support

Encode the radiocore's address into the application's DT as the
application needs to instruct IRONside SE about where the radiocore
should be booted from.

Upstream PR #: 89009

Signed-off-by: Sebastian Bøe <[email protected]>

Author: SebastianBoe

boards/nordic/nrf54h20dk/nrf54h20dk_nrf54h20_cpuapp_iron.dts

@@ -52,6 +52,10 @@
 			reg = <0xe4000 DT_SIZE_K(64)>;
 		};
 
+		cpurad_slot0_partition: partition@54000 {
+			reg = <0x54000 DT_SIZE_K(256)>;
+		};
+
 		cpuflpr_code_partition: partition@f4000 {
 			reg = <0xf4000 DT_SIZE_K(48)>;
 		};