[nrf noup] booutil: loader: Fixup for NSIB and multi-image

Commit 8fe7070 broke bootloader updates
for nRF91 and non-multi image builds. This commit is fixing this by
restoring the previous functionality and `ifdef` out the new logic
needed for multi-image.

Ref. NCSDK-23305

Signed-off-by: Sigvart Hovland <sigvart.hovland@nordicsemi.no>
(cherry picked from commit 7429a98)
Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>

boot/bootutil/src/loader.c

@@ -967,7 +967,6 @@ boot_validated_swap_type(struct boot_loader_state *state,
  if(reset_addr < PM_CPUNET_B0N_ADDRESS)
 #endif
  {
- const struct flash_area *nsib_fa;
  const struct flash_area *primary_fa;
  rc = flash_area_open(flash_area_id_from_multi_image_slot(
  BOOT_CURR_IMG(state), BOOT_PRIMARY_SLOT),
@@ -978,6 +977,9 @@ boot_validated_swap_type(struct boot_loader_state *state,
 
  /* Check start and end of primary slot for current image */
  if (reset_addr < primary_fa->fa_off) {
+#if defined(CONFIG_SOC_NRF5340_CPUAPP) && defined(CONFIG_NRF53_MULTI_IMAGE_UPDATE)
+ const struct flash_area *nsib_fa;
+
  /* NSIB upgrade slot */
  rc = flash_area_open((uint32_t)_image_1_primary_slot_id,
  &nsib_fa);
@@ -992,6 +994,10 @@ boot_validated_swap_type(struct boot_loader_state *state,
  /* Set primary to be NSIB upgrade slot */
  BOOT_IMG_AREA(state, 0) = nsib_fa;
  }
+#else
+ return BOOT_SWAP_TYPE_NONE;
+#endif
+
  } else if (reset_addr > (primary_fa->fa_off + primary_fa->fa_size)) {
  /* The image in the secondary slot is not intended for any */
  return BOOT_SWAP_TYPE_NONE;