cgroup/cpuset: move v1 interfaces to cpuset-v1.c

Move legacy cpuset controller interfaces files and corresponding code
into cpuset-v1.c. 'update_flag', 'cpuset_write_resmask' and
'cpuset_common_seq_show' are also used for v1, so declare them in
cpuset-internal.h.

'cpuset_write_s64', 'cpuset_read_s64' and 'fmeter_getrate' are only used
cpuset-v1.c now, make it static.

Signed-off-by: Chen Ridong <chenridong@huawei.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>