arm: mm: Define set_memory_* functions for ARM

Other architectures define various set_memory functions to allow
attributes to be changed (e.g. set_memory_x, set_memory_rw, etc.)
Currently, these functions are missing on ARM. Define these in an
appropriate manner for ARM.

Change-Id: I5083aa985d31e195f138ce7ed26d2a1d4b80faae
CRs-Fixed: 498398
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>