Skip reserving memory for non-executable and BL3-0 images

This patch adds support to not reserve the memory where an image is
loaded if the image is:

  1. A non-executable image e.g. a certificate
  2. An executable image which is not meant to run on the
     application CPU (e.g. BL3-0)

Both types of images are characterized by a NULL entrypoint argument
to the load_image() function. It is used to distinguish them from
other type of images.

Important: Use this feature carefully. The caller is responsible for
providing a valid entrypoint while loading images which will execute
on the application CPU to prevent a potential overwrite of the
corresponding memory region.

Change-Id: Ied482280d9db714c529ec12c33a6c1d918d77a4e

common/bl_common.c

@@ -275,9 +275,16 @@ int load_image(meminfo_t *mem_layout,
 	 * Update the memory usage info.
 	 * This is done after the actual loading so that it is not updated when
 	 * the load is unsuccessful.
+	 * If the caller does not provide an entry point, bypass the memory
+	 * reservation.
 	 */
+	if (entry_point_info != NULL) {
 		reserve_mem(&mem_layout->free_base, &mem_layout->free_size,
 				image_base, image_size);
+	} else {
+		INFO("Skip reserving memory: 0x%lx - 0x%lx\n",
+				image_base, image_base + image_size);
+	}
 
 	image_data->image_base = image_base;
 	image_data->image_size = image_size;