Revert "parisc: Use ldcw instruction for SMP spinlock release barrier"

This reverts commit 9e5c6021

.
No need to use the ldcw instruction as SMP spinlock release barrier.
Revert it to gain back speed again.

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