sw64: add SIMD emulation for guest IO access

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I56WV8



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To support SIMD IO access in guest, an exception type IF_SIMDEMU has
been added in do_entIF(), which is used to emualte SIMD load/store.

Currently, only vldd and vstd are supported for emulation.

Signed-off-by: Lu Feifei <lufeifei@wxiat.com>
Reviewed-by: He Sheng <hesheng@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>