target/loongarch: Implement xvfcmp

This patch includes:
- XVFCMP.cond.{S/D}.

Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230914022645.1151356-50-gaosong@loongson.cn>
5 files changed