[CIFS] Add mmap for direct, nobrl cifs mount types

without mmap functions in file_ops OpenOffice can't save changes in
existing document. The same situation you can see with gedit. Also, a.out
format of files can't be executed without mmap.

Signed-off-by: Pavel Shilovsky <piastryyy@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>