libprocessgroup: Move CgroupSetupCgroups() to libprocessgroup_setup

Only init uses SetupCgroups. This functionality is
moved from libprocessgroup to its own library, and only
init links to it.

Also, merge CgroupSetupCgroups() with CgroupMap::SetupCgroups()
because the former is just an alias of the latter, and
CgroupMap does not belong to libcgrouprc_setup.

Test: boots
Bug: 123664216
Change-Id: I941dc0c415e2b22ae663d43e30dc7a464687325e
Merged-In: I941dc0c415e2b22ae663d43e30dc7a464687325e