sparc64: Add membar to Niagara2 memcpy code.

This is the prevent previous stores from overlapping the block stores
done by the memcpy loop.

Based upon a glibc patch by Jose E. Marchesi
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/lib/NG2memcpy.S

@@ -236,6 +236,7 @@ FUNC_NAME:	/* %o0=dst, %o1=src, %o2=len */
 	 */
 	VISEntryHalf
 
+	membar		#Sync
 	alignaddr	%o1, %g0, %g0
 
 	add		%o1, (64 - 1), %o4