LoongArch: Increase max supported CPUs up to 2048

LoongArch: Increase max supported CPUs up to 2048

Increase max supported CPUs up to 2048, including:
1. Increase CSR.CPUID register's effective width;
2. Define MAX_CORE_PIC (a.k.a. max physical ID) to 2048;
3. Allow NR_CPUS (a.k.a. max logical ID) to be as large as 2048;
4. Introduce acpi_numa_x2apic_affinity_init() to handle ACPI SRAT
   for CPUID >= 256.

Note: The reason of increasing to 2048 rather than 4096/8192 is because
      the IPI hardware can only support 2048 as a maximum.

Reviewed-by: Yanteng Si <si.yanteng@linux.dev>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>