ux500: rework device registration

Change the Ux500 devices to be dynamically allocated and added by
calling functions instead of referencing structures, thereby allowing
5500 and other derivatives' support to be added without having to
duplicate structures, use fixup functions, or use compile-time macros.

Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>