[nrf fromlist] boards: nordic: Add reserved partitions for IronSide SE

Upstream PR #: 99199

Add a self-documenting devicetree node, to communicate how much memory
is reserved for this firmware, in the default memory map file of each
supported board.

Signed-off-by: Grzegorz Swiderski <[email protected]>
(cherry picked from commit a41242398d300317fd027fd73d8e933ccf21b049)

Author: 57300

boards/nordic/nrf54h20dk/nrf54h20dk_nrf54h20-memory_map.dtsi

@@ -131,6 +131,10 @@
 		#address-cells = <1>;
 		#size-cells = <1>;
 
+		ironside_se_reserved: partition@0 {
+			reg = <0x0 DT_SIZE_K(192)>;
+		};
+
 		cpuapp_boot_partition: partition@30000 {
 			reg = <0x30000 DT_SIZE_K(64)>;
 		};

boards/nordic/nrf9280pdk/nrf9280pdk_nrf9280-memory_map_iron.dtsi

@@ -47,6 +47,10 @@
 		#address-cells = <1>;
 		#size-cells = <1>;
 
+		ironside_se_reserved: partition@0 {
+			reg = <0x0 DT_SIZE_K(192)>;
+		};
+
 		cpuapp_boot_partition: partition@312000 {
 			reg = <0x312000 DT_SIZE_K(64)>;
 		};