boards: nordic: add periphconf_partition to memory map for nRF9280

- nRF9280 memory_map_iron is missing periphconf_partition, added this
  partition to mram11 at address 0xe60a000.

Signed-off-by: Aymen LAOUINI <[email protected]>

Author: ayla-nordicsemi

boards/nordic/nrf9280pdk/nrf9280pdk_nrf9280-memory_map_iron.dtsi

@@ -75,5 +75,9 @@
 		storage_partition: partition@600000 {
 			reg = <0x600000 DT_SIZE_K(40)>;
 		};
+
+		periphconf_partition: partition@60a000 {
+			reg = <0x60a000 DT_SIZE_K(8)>;
+		};
 	};
 };