s390/barrier: factor out bcr_serialize()

Factor out bcr_serialize() inline assembly function which describes
what the bcr instruction is used for.
Use bcr_serialize() like before in mb(), but also in upcoming changes.
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/barrier.h

@@ -16,20 +16,24 @@
 
 #ifdef CONFIG_HAVE_MARCH_Z196_FEATURES
 /* Fast-BCR without checkpoint synchronization */
-#define __ASM_BARRIER "bcr 14,0\n"
+#define __ASM_BCR_SERIALIZE "bcr 14,0\n"
 #else
-#define __ASM_BARRIER "bcr 15,0\n"
+#define __ASM_BCR_SERIALIZE "bcr 15,0\n"
 #endif
 
-#define mb() do {  asm volatile(__ASM_BARRIER : : : "memory"); } while (0)
+static __always_inline void bcr_serialize(void)
+{
+	asm volatile(__ASM_BCR_SERIALIZE : : : "memory");
+}
 
-#define rmb()				barrier()
-#define wmb()				barrier()
-#define dma_rmb()			mb()
-#define dma_wmb()			mb()
-#define __smp_mb()			mb()
-#define __smp_rmb()			rmb()
-#define __smp_wmb()			wmb()
+#define mb()		bcr_serialize()
+#define rmb()		barrier()
+#define wmb()		barrier()
+#define dma_rmb()	mb()
+#define dma_wmb()	mb()
+#define __smp_mb()	mb()
+#define __smp_rmb()	rmb()
+#define __smp_wmb()	wmb()
 
 #define __smp_store_release(p, v)					\
 do {									\