Revert "sw64: clean up unused single step support in kernel"

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



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This reverts commit a11aeaf7.

lldb depends on PTRACE_SINGLESTEP, so revert the code to keep
compatibility.

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