target/loongarch: Implement xvseq xvsle xvslt

This patch includes:
- XVSEQ[I].{B/H/W/D};
- XVSLE[I].{B/H/W/D}[U];
- XVSLT[I].{B/H/W/D/}[U].

Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230914022645.1151356-49-gaosong@loongson.cn>