cpuset: add cpuset1_init helper for v1 initialization

cpuset: add cpuset1_init helper for v1 initialization

This patch introduces the cpuset1_init helper in cpuset_v1.c to initialize
v1-specific fields, including the fmeter and relax_domain_level members.

The relax_domain_level related code will be moved to cpuset_v1.c in a
subsequent patch. After this move, v1-specific members will only be
visible when CONFIG_CPUSETS_V1=y.

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