xfs: remove the XFS_IOC_{ALLOC,FREE}SP* definitions

Now that we've made these ioctls defunct, move them from xfs_fs.h to
xfs_ioctl.c, which effectively removes them from the publicly supported
ioctl interfaces for XFS.

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