target/loongarch: Implement vhaddw/vhsubw

This patch includes:
- VHADDW.{H.B/W.H/D.W/Q.D/HU.BU/WU.HU/DU.WU/QU.DU};
- VHSUBW.{H.B/W.H/D.W/Q.D/HU.BU/WU.HU/DU.WU/QU.DU}.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20230504122810.4094787-9-gaosong@loongson.cn>
5 files changed