s390/mm: Select ARCH_WANT_IRQS_OFF_ACTIVATE_MM

Select ARCH_WANT_IRQS_OFF_ACTIVATE_MM so that activate_mm() is called with
irqs disabled. This allows to call switch_mm_irqs_off() instead of
switch_mm() and saves two local_irq_save() / local_irq_restore() pairs.

Reviewed-by: Alexander Gordeev <[e-mail]>
Signed-off-by: Heiko Carstens <[e-mail]>

arch/s390/Kconfig

···
 	select ARCH_WANTS_NO_INSTR
 	select ARCH_WANT_DEFAULT_BPF_JIT
 	select ARCH_WANT_IPC_PARSE_VERSION
+	select ARCH_WANT_IRQS_OFF_ACTIVATE_MM
 	select ARCH_WANT_KERNEL_PMD_MKWRITE
 	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP

arch/s390/include/asm/mmu_context.h

···
 static inline void activate_mm(struct mm_struct *prev,
                                struct mm_struct *next)
 {
-	unsigned long flags;
-
-	switch_mm(prev, next, current);
+	switch_mm_irqs_off(prev, next, current);
 	cpumask_set_cpu(smp_processor_id(), mm_cpumask(next));
-	local_irq_save(flags);
 	if (test_thread_flag(TIF_ASCE_PRIMARY))
 		local_ctl_load(1, &get_lowcore()->kernel_asce);
 	else
 		local_ctl_load(1, &get_lowcore()->user_asce);
 	local_ctl_load(7, &get_lowcore()->user_asce);
-	local_irq_restore(flags);
 }
 
 #include <asm-generic/mmu_context.h>