util/mmap-alloc: qemu_fd_getfs() This new helper fetches file system type for a fd. Only Linux is implemented so far. Currently only tmpfs and hugetlbfs are defined, but it can grow as needed. Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Juan Quintela <quintela@redhat.com> Signed-off-by: Juan Quintela <quintela@redhat.com>