MIPS: Loongson64: Switch to SYNC_R4K

Nowadays SYNC_R4K is performing better than Loongson64's
custom sync mechanism.

Switch to SYNC_R4K to improve performance and reduce code
duplication.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/smp.h

@@ -50,7 +50,6 @@ extern int __cpu_logical_map[NR_CPUS];
 #define SMP_CALL_FUNCTION	0x2
 /* Octeon - Tell another core to flush its icache */
 #define SMP_ICACHE_FLUSH	0x4
-#define SMP_ASK_C0COUNT		0x8
 
 /* Mask of CPUs which are currently definitely operating coherently */
 extern cpumask_t cpu_coherent_mask;