sw64: reimplement save_stack_trace()

Sunway inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5GFQQ



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It used to save stack-backtrace addresses by SP, which is inaccurate.
In order to implement this function accurately, we provide two ways
to support it.

Signed-off-by: Wu Liliu <wuliliu@wxiat.com>

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