Add a mount option 'fsc' to enable local caching on CIFS.

I considered adding a separate debug bit for caching, but it appears that
debugging would be relatively easier with the normal CIFS_INFO level.

As the cifs-utils (userspace) changes are not done yet, this patch enables
'fsc' by default to enable testing.
Signed-off-by: NSuresh Jayaraman <sjayaraman@suse.de>
Acked-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NSteve French <sfrench@us.ibm.com>