xfs: fully support v5 format filesystems

We have had this code in the kernel for over a year now and have
shaken all the known issues out of the code over the past few
releases. It's now time to remove the experimental warnings during
mount and fully support the new filesystem format in production
systems.

Remove the experimental warning, and add a version number to the
initial "mounting filesystem" message to tell use what type of
filesystem is being mounted. Also, remove the temporary inode
cluster size output at mount time now we know that this code works
fine.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>