Revert "parisc: Drop LDCW barrier in CAS code when running UP"

commit 462fb756 upstream.

This reverts commit e6eb5fe9

.
We need to optimize it differently. A follow up patch will correct it.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: <stable@vger.kernel.org> # v5.2+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>