sw64: simplify and improve smp operations

Sunway inclusion
category: performance
bugzilla: https://gitee.com/openeuler/kernel/issues/I73KT3



--------------------------------

This patch:
  - Clean up redundant struct smp_ops.
  - smp_send_stop wait up to one second for other CPUs to stop.
  - Mark cpu offline on reception of IPI_CPU_STOP.

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