target/loongarch: Implement vsadd/vssub

This patch includes:
- VSADD.{B/H/W/D}[U];
- VSSUB.{B/H/W/D}[U].

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20230504122810.4094787-8-gaosong@loongson.cn>
3 files changed