boards: nordic: add partitions to memory map for nRF9280

- nRF9280 memory_map_iron is missing periphconf_partition, added this
  partition to mram11 at address 0xe60a000.
- Add secure_storage_partition at 0xe60c000 to memory map. This
  partition is devided in two: cpuapp_crypto_partition and
  cpuapp_its_partition, both are 4KB. Those partitions are used
  by gen_uicr.py script to generate the UICR file.

Signed-off-by: Aymen LAOUINI <aymen.laouini@nordicsemi.no>