Split and merge in Coarse provider to enable IPC API

Coarse provider has to always call:
- umfMemoryProviderAllocationSplit(upstream_provider) or
- umfMemoryProviderAllocationMerge(upstream_provider)
when splitting or merging memory blocks,
because the IPC API would not work on split/merged memory
blocks otherwise.

Signed-off-by: Lukasz Dorau <[email protected]>

Author: ldorau