sparc64: Provide cmpxchg64()

sparc64 allmodconfig:

drivers/block/blockconsole.c: In function ‘bcon_advance_console_bytes’:
drivers/block/blockconsole.c:164: error: implicit declaration of function ‘cmpxchg64’

Map cmpxchg64() to cmpxchg64_local() (which eventually calls
__cmpxchg_u64()) to fix this.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/include/asm/cmpxchg_64.h

@@ -141,5 +141,6 @@ static inline unsigned long __cmpxchg_local(volatile void *ptr,
 	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\
 	cmpxchg_local((ptr), (o), (n));					\
   })
+#define cmpxchg64(ptr, o, n)	cmpxchg64_local((ptr), (o), (n))
 
 #endif /* __ARCH_SPARC64_CMPXCHG__ */