There is no way to build  U8500 kernels without an MMU
at this point because of dependencies on MMU-only functions.

As long as nobody is interested in fixing this, let's just disable
the platforms for nommu kernels.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NMathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>