libxfs: disallow filesystems with reverse mapping and reflink and realtime

libxfs: disallow filesystems with reverse mapping and reflink and realtime

Neither the kernel nor the code in xfsprogs support filesystems that
have (either reverse mapping btrees or reflink) enabled and a realtime
volume configured.  The kernel rejects such combinations and mkfs
refuses to format such a config, but xfsprogs doesn't check and can do
Bad Things, so port those checks before someone shreds their filesystem.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>