zephyr: arm: Update reading the flash image reset vector

This change uses the flash functions to read the applications
reset vector. This allow flexibility on which flash device the
application is programmed.
For e.g: MCUBoot can be programmed and running from Internal
Flash while Zephyr can be loaded from a different Flash device.
This change is made for ARM platform, it can be extended to
non-ARM platforms as well.

Signed-off-by: Mahesh Mahadevan <mahesh.mahadevan@nxp.com>

boot/zephyr/flash_map_extended.c

@@ -141,8 +141,12 @@ int flash_area_sector_from_off(off_t off, struct flash_sector *sector)
 
 uint8_t flash_area_get_device_id(const struct flash_area *fa)
 {
-	(void)fa;
-	return FLASH_DEVICE_ID;
+#if defined(CONFIG_ARM)
+    return fa->fa_id;
+#else
+    (void)fa;
+    return FLASH_DEVICE_ID;
+#endif
 }
 
 #define ERASED_VAL 0xff

boot/zephyr/main.c

@@ -157,16 +157,26 @@ static void do_boot(struct boot_rsp *rsp)
     /* Get ram address for image */
     vt = (struct arm_vector_table *)(rsp->br_hdr->ih_load_addr + rsp->br_hdr->ih_hdr_size);
 #else
-    uintptr_t flash_base;
     int rc;
+    const struct flash_area *fap;
+    static uint32_t dst[2];
 
     /* Jump to flash image */
-    rc = flash_device_base(rsp->br_flash_dev_id, &flash_base);
+    rc = flash_area_open(rsp->br_flash_dev_id, &fap);
+    assert(rc == 0);
+
+    rc = flash_area_read(fap, rsp->br_hdr->ih_hdr_size, dst, sizeof(dst));
     assert(rc == 0);
+#ifndef CONFIG_ASSERT
+    /* Enter a lock up as asserts are disabled */
+    if (rc != 0) {
+        while (1);
+    }
+#endif
+
+    flash_area_close(fap);
 
-    vt = (struct arm_vector_table *)(flash_base +
-                                     rsp->br_image_off +
-                                     rsp->br_hdr->ih_hdr_size);
+    vt = (struct arm_vector_table *)dst;
 #endif
 
     if (IS_ENABLED(CONFIG_SYSTEM_TIMER_HAS_DISABLE_SUPPORT)) {