device_tree/fit: Constify data structures

* Add const quailifier to arguments and elements.
* Add casts where necessary in cn81xx/soc.

Tested on Cavium CN81xx EVB SFF.

Change-Id: Id27966427fb97457fe883be32685d1397fb0781f
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/28267
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
6 files changed