kernel: fix mips MT_SMP kernel crash on cache flush

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/generic/patches-4.4/100-MIPS-fix-MT_SMP-cacheflush.patch

+Fix crash on cache flush with the MT_SMP variant
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+
+--- a/arch/mips/mm/c-r4k.c
++++ b/arch/mips/mm/c-r4k.c
+@@ -60,8 +60,10 @@ static inline void r4k_on_each_cpu(void
+ 	 * to restrict that call when a CM is not present because both
+ 	 * CM-based SMP protocols (CMP & CPS) restrict index-based cache ops.
+ 	 */
++#ifndef CONFIG_MIPS_MT_SMP
+ 	if (!mips_cm_present())
+ 		smp_call_function_many(&cpu_foreign_map, func, info, 1);
++#endif
+ 	func(info);
+ 	preempt_enable();
+ }