sw64: ensure IRQs are off when switch/load/activate mm context

Sunway inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5PNEN



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This is because of commit f98db601 ("sched/core: Add switch_mm_irqs_off()
and use it in the scheduler") in which switch_mm_irqs_off() is called by the
scheduler, vs switch_mm() which is used by use_mm().

This patch mirrors the x86 code, ie. it disables interrupt in switch_mm(), and
optimises the scheduler case by defining switch_mm_irqs_off(). After that, the
asn_lock and need_new_asn in cpu_data are no longer needed.

This patch also moves __load_new_mm_context() into flush_tlb_current() and make
sure IRQs are off over it.

Signed-off-by: He Sheng <hesheng@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>