xfs: untangle the open zones reporting in mountinfo

xfs: untangle the open zones reporting in mountinfo

Keeping a value per line makes parsing much easier, so move the maximum
number of open zones into a separate line, and also add a new line for
the number of open open GC zones.  While that has to be either 0 or 1
currently having a value future-proofs the interface for adding more open
GC zones if needed.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>