target/loongarch: Add function to check current arch

target/loongarch: Add function to check current arch

Add is_la64 function to check if the current cpucfg[1].arch equals to
2(LA64).

Signed-off-by: Jiajie Chen <c@jia.je>
Co-authored-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Song Gao <gaosong@loongson.cn>
Message-ID: <20230817093121.1053890-2-gaosong@loongson.cn>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230821125959.28666-7-philmd@linaro.org>