sepolicy support for cgroup v2

cgroup v2 is going to be used for freezer v2 support. The cgroup v2 hiearchy
will be mounted by init under /sys/fs/cgroup hence proper access rights
are necessary for sysfs. After mounting, the cgroup v2 kernfs will use
the label cgroup_v2 and system_manager will handle the freezer

Bug: 154548692
Test: verified that files undes sysfs and cgroup v2 kernfs are accessed
as required to allow proper functioning for the freezer.

Change-Id: Idfb3f6e77b60dad032d1e306d2f9b58cd5775960
7 files changed