cma: Drop alignment requirements for regions not in system

CMA requires that regions be aligned to page block order or higher
to ensure migration types can be changed for whole regions. This
is not applicable if the memory is removed from the system completely.
Keep the alignment requirement at PAGE_SIZE if the memory is outside
the system allocator. Note that if there are alignment requirements
these can still be set up by manually aligning the base/size.

Change-Id: I316008095469492c150e8b69bb20b369579e3a36
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>