LoongArch: Parsing CPU-related information from DTS

Generally, we can get cpu-related information, such as model name, from
/proc/cpuinfo. For FDT-based systems, we need to parse the relevant
information from DTS.

BTW, set loongson_sysconf.cores_per_package to num_processors if SMBIOS
doesn't provide a valid number (usually FDT-based systems).

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Signed-off-by: Hongliang Wang <wanghongliang@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>