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

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

BugLink: https://bugs.launchpad.net/bugs/1892417
commit 462fb756c7de1ffe5bc6099149136031c2d9c02a upstream.

This reverts commit e6eb5fe9123f05dcbf339ae5c0b6d32fcc0685d5.
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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>