sw64: always use cpu_data and simplify it

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I56OLG



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Make use of cpu_data no matter SMP is yes or no, and remove unused
fields from it. After that, some function calls can be simplified.

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