arch: tile: include: asm: add cmpxchg64() definition

Need add cmpxchg64(), or will cause compiling issue.

Need define it as cmpxchg() only for 64-bit operation, since cmpxchg()
can support 8 bytes.

The related error (with allmodconfig):

drivers/block/blockconsole.c: In function ‘bcon_advance_console_bytes’:
drivers/block/blockconsole.c:164:2: error: implicit declaration of function ‘cmpxchg64’ [-Werror=implicit-function-declaration]

Signed-off-by: Chen Gang <[e-mail]>
Signed-off-by: Chris Metcalf <[e-mail]>

arch/tile/include/asm/cmpxchg.h

···
 
 #define tas(ptr) (xchg((ptr), 1))
 
+#define cmpxchg64(ptr, o, n)						\
+({									\
+	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\
+	cmpxchg((ptr), (o), (n));					\
+})
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_TILE_CMPXCHG_H */