NFSv4: Define an fs_locations bitmap

This is (similar to getattr bitmap) but includes fs_locations and
mounted_on_fileid attributes. Use this bitmap for encoding in fs_locations
requests.
Note: We can probably do better by requesting locations as part of fsinfo
itself.

Signed-off-by: Manoj Naik <manoj@almaden.ibm.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>