xfs: move eofblocks conversion function to xfs_ioctl.c

Move xfs_fs_eofblocks_from_user into the only file that actually uses
it, so that we don't have this function cluttering up the header file.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>