cma: Allow option to use strict memblock_reserved memory

Despite all the performance optimizations, some clients are
still unable to use CMA because of the allocation latency.
Rather than make those clients use a separate set of APIs,
extend the CMA code to allow clients to keep the memory out of
the buddy allocator. Since the pages never actually go to the
buddy allocator, allocation and freeing is only based on the bitmap
allocator to find the appropriate region.

Change-Id: Ia31bb1212fd7b19280361128453c8d25369ce592
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>