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+