target/loongarch: Add generic CPU model information On LoongArch system, CPU model name comes from IOCSR register LOONGARCH_IOCSR_VENDOR and LOONGARCH_IOCSR_CPUNAME. Its value can be initialized when CPU is created. Signed-off-by: Bibo Mao <maobibo@loongson.cn> Reviewed-by: Song Gao <gaosong@loongson.cn> Signed-off-by: Song Gao <gaosong@loongson.cn>