target/loongarch: Add avail_64 to check la64-only instructions

The la32 instructions listed in Table 2 at
https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#overview-of-basic-integer-instructions

Co-authored-by: Jiajie Chen <c@jia.je>
Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20230822032724.1353391-9-gaosong@loongson.cn>
Message-Id: <20230822071959.35620-3-philmd@linaro.org>
10 files changed