ARM: mm: fix set_memory_*() bounds checks

The set_memory_*() bounds checks are buggy on several fronts:

1. They fail to round the region size up if the passed address is not
   page aligned.
2. The region check was incomplete, and didn't correspond with what
   was being asked of apply_to_page_range()

So, rework change_memory_common() to fix these problems, adding an
"in_region()" helper to determine whether the start & size fit within
the provided region start and stop addresses.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>