Revert "s390/spinlock: add gmb memory barrier"

CVE-2017-5753 (revert embargoed)
CVE-2017-5715 (revert embargoed)

This reverts commit 087580bf.
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/s390/include/asm/barrier.h

@@ -7,8 +7,6 @@
 #ifndef __ASM_BARRIER_H
 #define __ASM_BARRIER_H
 
-#include <asm/alternative.h>
-
 /*
  * Force strict CPU ordering.
  * And yes, this is required on UP too when we're talking
@@ -24,14 +22,6 @@
 
 #define mb() do {  asm volatile(__ASM_BARRIER : : : "memory"); } while (0)
 
-static inline void gmb(void)
-{
-	asm volatile(
-		ALTERNATIVE("", ".long 0xb2e8f000", 81)
-		: : : "memory");
-}
-#define gmb gmb
-
 #define rmb()				barrier()
 #define wmb()				barrier()
 #define dma_rmb()			mb()