ARM: ux500: Disable platform setup of the ab8500 when DT is enabled

The final piece of the ab8500 puzzle. Here we prevent any of the ab8500-*
drivers from being registered from platform code when Device Tree is
enabled, as we expect DT do probe each of these individually. We also
provide the relevant compatible strings, so that DT knows which nodes
it needs to pay attention to during population.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>