LoongArch: optimize for syscall return

LoongArch inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I6BWFP



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If the syscall is not rt_sigreturn,there is no need to do
RESTORE_STATIC and RESTORE_TEMP.

Signed-off-by: Hongchen Zhang <zhanghongchen@loongson.cn>
Change-Id: I61804bb16ce678dd39e9f197bd88d91e13b972cb
(cherry picked from commit eba5f68c)