target/loongarch: Implement xvhaddw/xvhsubw

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

Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230914022645.1151356-20-gaosong@loongson.cn>
4 files changed