[nrf noup] boot: zephyr: let secondary_1 slot be in regular flash

Added support for multi-image DFU for nRF53 from internal flash which
requires the region parameter of `mcuboot_secondary_1` to be
configurable. So that the `mcuboot_secondary_1` partition is put into
internal flash.

Ref. NCSDK-12809

Signed-off-by: Sigvart Hovland <sigvart.hovland@nordicsemi.no>

boot/zephyr/pm.yml

@@ -81,7 +81,12 @@ mcuboot_primary_1:
 
 #if (CONFIG_NRF53_MULTI_IMAGE_UPDATE)
 mcuboot_secondary_1:
+ #if (CONFIG_PM_EXTERNAL_FLASH_MCUBOOT_SECONDARY_1)
  region: external_flash
+ #endif /* CONFIG_PM_EXTERNAL_FLASH_MCUBOOT_SECONDARY_1 */
  size: CONFIG_NRF53_RAM_FLASH_SIZE
+ placement:
+ after: mcuboot_secondary
+ align: {start: 4}
 
 #endif /* CONFIG_NRF53_MULTI_IMAGE_UPDATE */