cma: Add support for removed regions

In addition to reserving memory from the system, there may
be uses where memory should be completely removed from control
of the linux page allocator. Add the appropriate information to
be able to remove the memory.

Change-Id: Ia2e959e0858fb240ab5c0deee49b0d6e4aecfc00
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>