LoongArch: Add process management

Add process management support for LoongArch, including: thread info
definition, context switch and process tracing.

Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>