ANDROID: cgroups: add v2 freezer ABI changes

introduce the freezer_state struct to be used by the v2 freezer
backports

Test: built and booted
Bug: 163547360
Signed-off-by: Marco Ballesio <balejs@google.com>
Change-Id: I4705ee9787f35db58e27de339d5264d1cd45007a