1, We assume arch/loongarch/include/asm/smp.h be included in include/
   linux/smp.h is valid and the reverse inclusion isn't. So remove the
   <linux/smp.h> in arch/loongarch/include/asm/smp.h.
2, arch/loongarch/include/asm/smp.h is only needed when CONFIG_SMP,
   and setup.c include it only because it need plat_smp_setup(). So,
   reorganize setup.c & smp.h, and then remove <asm/smp.h> in setup.c.
3, Fix cacheinfo.c and percpu.h build error by adding the missing header
   files when !CONFIG_SMP.
4, Fix acpi.c build error by adding CONFIG_SMP guards.
5, Move irq_stat definition from smp.c to irq.c and fix its declaration.
6, Select CONFIG_SMP for CONFIG_NUMA, similar as other architectures do.
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>