target/loongarch: Implement vsat

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

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20230504122810.4094787-18-gaosong@loongson.cn>
5 files changed