ARM: realview: remove sparsemem hack

The realview-pbx platform has an elaborate way of avoiding the use of highmem
by redefining its phys_to_virt function. In practice this doesn't help all
that much, and it gets in the way of doing multiplatform builds for
realview.

This removes the feature and kills off the mach/memory.h file for realview.
We also lose the ability to do sparsemem with this patch, but that should
be put back into place for generic multiplatform configurations, to save
a little memory on PBX.

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