sw64: check processor state by user_mode(regs)

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



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The `regs->ps & 8` and `regs->ps & ~IPL_MAX` don't have a clear meaning.
We replace them with user_mode(regs) and !user_mode(regs), and reserve
regs->ps[63:4] for future extension.

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