target/loongarch: Implement vfrstp

This patch includes:
- VFRSTP[I].{B/H}.

Acked-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20230504122810.4094787-33-gaosong@loongson.cn>
diff --git a/target/loongarch/helper.h b/target/loongarch/helper.h
index 75120ca..2cc235d 100644
--- a/target/loongarch/helper.h
+++ b/target/loongarch/helper.h
@@ -512,3 +512,8 @@
 DEF_HELPER_FLAGS_4(vbitrevi_h, TCG_CALL_NO_RWG, void, ptr, ptr, i64, i32)
 DEF_HELPER_FLAGS_4(vbitrevi_w, TCG_CALL_NO_RWG, void, ptr, ptr, i64, i32)
 DEF_HELPER_FLAGS_4(vbitrevi_d, TCG_CALL_NO_RWG, void, ptr, ptr, i64, i32)
+
+DEF_HELPER_4(vfrstp_b, void, env, i32, i32, i32)
+DEF_HELPER_4(vfrstp_h, void, env, i32, i32, i32)
+DEF_HELPER_4(vfrstpi_b, void, env, i32, i32, i32)
+DEF_HELPER_4(vfrstpi_h, void, env, i32, i32, i32)