target/loongarch: Implement vext2xv

This patch includes:
- VEXT2XV.{H/W/D}.B, VEXT2XV.{HU/WU/DU}.BU;
- VEXT2XV.{W/D}.B, VEXT2XV.{WU/DU}.HU;
- VEXT2XV.D.W, VEXT2XV.DU.WU.

Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230914022645.1151356-31-gaosong@loongson.cn>
5 files changed