documnt FMODE_ constants

commit fc9161e54d0dbf799beff9692ea1cc6237162b85 upstream.

Make sure all FMODE_ constants are documents, and ensure a coherent
style for the already existing comments.

[This is needed for the next patch in the .27 kernel which
 changes fs.h.  This patch makes it easier to handle. - gkh]

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>