ARM: ux500: Only initialise STE's UIBs on boards which support them

ST-Ericsson uses User Interface Boards to extend functionality of
some of their development boards. However, these aren't compatible
with all the supported boards found in Mainline (Snowball for
instance). This patch ensures that the UIBs are only probed on
boards which can actually support them. This in turn saves lots of
unnecessary error messages normally found in Snowball's boot log.

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>