ion: Add support for dynamic carveout heaps

The memory regions managed by carveout heaps are provisioned to
the heaps at boot, and once a memory region is bound to a heap,
the binding of heap to memory region is immutable. In some cases,
it might be desireable to assign the memory region for a carveout
heap on demand.

Thus, add support for dynamic carveout heaps. Dynamic carveout heaps
are initialized as empty heaps (i.e. they have no memory associated
with them) and must have memory added to them prior to use. Dynamic
heaps can also have memory removed from them, so add support for both
of these functionalities as well.

Change-Id: Icafe83c879e7f5a10a92dd1fcd97f1fda2b02c20
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>