[noup] booutil: loader: Do not check reset vector for XIP image

The XIP image, 2, does not have reset vector.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>

boot/bootutil/src/loader.c

@@ -816,6 +816,16 @@ boot_validate_slot(struct boot_loader_state *state, int slot,
  * overwriting an application written to the incorrect slot.
  * This feature is only supported by ARM platforms.
  */
+#if MCUBOOT_IMAGE_NUMBER >= 3
+ /* Currently the MCUboot can be configured for up to 3 image, where image number 2 is
+ * designated for XIP, where it is the second part of image stored in slots of image
+ * 0. This part of image is not bootable, as the XIP setup is done by the app in
+ * image 0 slot, and it does not carry the reset vector.
+ */
+ if (area_id == FLASH_AREA_IMAGE_SECONDARY(2)) {
+ goto out;
+ }
+#endif
  if (area_id == FLASH_AREA_IMAGE_SECONDARY(BOOT_CURR_IMG(state))) {
  const struct flash_area *pri_fa = BOOT_IMG_AREA(state, BOOT_PRIMARY_SLOT);
  struct image_header *secondary_hdr = boot_img_hdr(state, slot);