cpumask: use mm_cpumask() wrapper: arm

Makes code futureproof against the impending change to mm->cpu_vm_mask.

It's also a chance to use the new cpumask_ ops which take a pointer
(the older ones are deprecated, but there's no hurry for arch code).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
index bcdb929..de6cefb 100644
--- a/arch/arm/include/asm/mmu_context.h
+++ b/arch/arm/include/asm/mmu_context.h
@@ -103,14 +103,15 @@
 
 #ifdef CONFIG_SMP
 	/* check for possible thread migration */
-	if (!cpus_empty(next->cpu_vm_mask) && !cpu_isset(cpu, next->cpu_vm_mask))
+	if (!cpumask_empty(mm_cpumask(next)) &&
+	    !cpumask_test_cpu(cpu, mm_cpumask(next)))
 		__flush_icache_all();
 #endif
-	if (!cpu_test_and_set(cpu, next->cpu_vm_mask) || prev != next) {
+	if (!cpumask_test_and_set_cpu(cpu, mm_cpumask(next)) || prev != next) {
 		check_context(next);
 		cpu_switch_mm(next->pgd, next);
 		if (cache_is_vivt())
-			cpu_clear(cpu, prev->cpu_vm_mask);
+			cpumask_clear_cpu(cpu, mm_cpumask(prev));
 	}
 #endif
 }