util: vfio-helpers: Factor out and fix processing of existing ram blocks

util: vfio-helpers: Factor out and fix processing of existing ram blocks

Factor it out into common code when a new notifier is registered, just
as done with the memory region notifier. This keeps logic about how to
process existing ram blocks at a central place.

Just like when adding a new ram block, we have to register the max_length.
Ram blocks are only "fake resized". All memory (max_length) is mapped.

Print the warning from inside qemu_vfio_ram_block_added().

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210429112708.12291-2-david@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>