multi-process: Synchronize remote memory

multi-process: Synchronize remote memory

Add ProxyMemoryListener object which is used to keep the view of the RAM
in sync between QEMU and remote process.
A MemoryListener is registered for system-memory AddressSpace. The
listener sends SYNC_SYSMEM message to the remote process when memory
listener commits the changes to memory, the remote process receives
the message and processes it in the handler for SYNC_SYSMEM message.

Signed-off-by: Jagannathan Raman <[email protected]>
Signed-off-by: John G Johnson <[email protected]>
Signed-off-by: Elena Ufimtseva <[email protected]>
Reviewed-by: Stefan Hajnoczi <[email protected]>
Message-id: 04fe4e6a9ca90d4f11ab6f59be7652f5b086a071.1611938319[email protected]
Signed-off-by: Stefan Hajnoczi <[email protected]>