Unexport some bits of linux/fs.h

There are some bits of linux/fs.h which are only used within the kernel and
shouldn't be in the UAPI.  Move these from uapi/linux/fs.h into linux/fs.h.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>