xfs: move symlink target write function to libxfs

Move xfs_symlink_write_target to xfs_symlink_remote.c so that kernel and
mkfs can share the same function.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

xfs: move remote symlink target read function to libxfs

Move xfs_readlink_bmap_ilocked to xfs_symlink_remote.c so that the
swapext code can use it to convert a remote format symlink back to
shortform format after a metadata repair. While we're at it, fix a
broken printf prefix.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

xfs: move xfs_symlink_remote.c declarations to xfs_symlink_remote.h

Move declarations for libxfs symlink functions into a separate header
file like we do for most everything else.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>