MIPS: Support CPU topology files in sysfs

This patch is prepared for Loongson's NUMA support, it offer meaningful
sysfs files such as physical_package_id, core_id, core_siblings and
thread_siblings in /sys/devices/system/cpu/cpu?/topology.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Reviewed-by: Andreas Herrmann <andreas.herrmann@caviumnetworks.com>
Cc: John Crispin <john@phrozen.org>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: linux-mips@linux-mips.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/7184/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>