xen: Introduce VGA sync dirty bitmap support This patch introduces phys memory client for Xen. Only sync dirty_bitmap and set_memory are actually implemented. migration_log will stay empty for the moment. Xen can only log one range for bit change, so only the range in the first call will be synced. Signed-off-by: Anthony PERARD <anthony.perard@citrix.com> Signed-off-by: Alexander Graf <agraf@suse.de>