xfs: introduce xfs_sb_is_v5 helper

Rather than open coding XFS_SB_VERSION_NUM(sbp) == XFS_SB_VERSION_5
checks everywhere, add a simple wrapper to encapsulate this and make
the code easier to read.

This allows us to remove the xfs_sb_version_has_v3inode() wrapper
which is only used in xfs_format.h now and is just a version number
check.

There are a couple of places where we should be checking the mount
feature bits rather than the superblock version (e.g. remount), so
those are converted to use xfs_has_crc(mp) instead.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>