target/loongarch: Implement vaddw/vsubw

This patch includes:
- VADDW{EV/OD}.{H.B/W.H/D.W/Q.D}[U];
- VSUBW{EV/OD}.{H.B/W.H/D.W/Q.D}[U];
- VADDW{EV/OD}.{H.BU.B/W.HU.H/D.WU.W/Q.DU.D}.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20230504122810.4094787-10-gaosong@loongson.cn>
5 files changed