feat(fwu): pass a const metadata structure to platform routines

The metadata structure copy is passed to the platform routine to set
the image source to boot the platform from. This is done by reading
the metadata structure. Pass the metadata as a read-only copy to the
routine -- the routine only needs to consume the metadata values and
should not be able to update the metadata fields.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Change-Id: I399cad99ab89c71483e5a32a1de0e22df304f8b0
diff --git a/plat/arm/common/arm_io_storage.c b/plat/arm/common/arm_io_storage.c
index 387086a..19ee1b0 100644
--- a/plat/arm/common/arm_io_storage.c
+++ b/plat/arm/common/arm_io_storage.c
@@ -217,7 +217,7 @@
  * bank to get its offset and length, and update these details in the I/O policy
  * of the FIP image.
  ******************************************************************************/
-void plat_fwu_set_images_source(struct fwu_metadata *metadata)
+void plat_fwu_set_images_source(const struct fwu_metadata *metadata)
 {
 	arm_set_fip_addr(metadata->active_index);
 }