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.

Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>