arm64: mm: kill mm_cpumask usage

mm_cpumask isn't actually used for anything on arm64, so remove all the
code trying to keep it up-to-date.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/smp.c

@@ -142,7 +142,6 @@ asmlinkage void secondary_start_kernel(void)
 	 */
 	atomic_inc(&mm->mm_count);
 	current->active_mm = mm;
-	cpumask_set_cpu(cpu, mm_cpumask(mm));
 
 	set_my_cpu_offset(per_cpu_offset(smp_processor_id()));
 	printk("CPU%u: Booted secondary processor\n", cpu);
@@ -233,12 +232,6 @@ int __cpu_disable(void)
 	 * OK - migrate IRQs away from this CPU
 	 */
 	migrate_irqs();
-
-	/*
-	 * Remove this CPU from the vm mask set of all processes.
-	 */
-	clear_tasks_mm_cpumask(cpu);
-
 	return 0;
 }