vfio: Introduce new files for VFIO MemoryListener

vfio: Introduce new files for VFIO MemoryListener

File "common.c" has been emptied of most of its definitions by the
previous changes and the only definitions left are related to the VFIO
MemoryListener handlers. Rename it to "listener.c" and introduce its
associated "vfio-listener.h" header file for the declarations.

Cleanup a little the includes while at it.

Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Avihai Horon <avihaih@nvidia.com>
Link: https://lore.kernel.org/qemu-devel/20250326075122.1299361-33-clg@redhat.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>