arc: Wire up cmpxchg64_local() to generic implementation

Provide cmpxchg64_local() for hexagon so we can start using it in
generic code.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

arch/arc/include/asm/cmpxchg.h

diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
index 76f43db..f2d5582 100644
--- a/arch/arc/include/asm/cmpxchg.h
+++ b/arch/arc/include/asm/cmpxchg.h
@@ -12,6 +12,7 @@
 
 #include <asm/barrier.h>
 #include <asm/smp.h>
+#include <asm-generic/cmpxchg-local.h>
 
 #ifdef CONFIG_ARC_HAS_LLSC
 
@@ -142,4 +143,6 @@
 
 #endif
 
+#define arch_cmpxchg64_local __generic_cmpxchg64_local
+
 #endif