sw64: perf: don't rely on layout of pt_regs to grab some registers

Sunway inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6ILAC



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The layout of struct perf_event_sw64_regs and pt_regs is inconsistent,
and some integer registers cannot get correct value.

This patch checks these registers explicitly to return the appropriate
values.

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