ANDROID: GKI: sched: stub sched_isolate symbols

These are needed to let modules load during compliance testing, but the
underlying core-isolation feature is not necessary for android-common.

Bug: 149816871
Test: compiled, checked abi diff for missing sched_*isolate* symbols
Signed-off-by: Quentin Perret <qperret@google.com>
Change-Id: Iaece1e98f821c50f2497b4a47b60714f49272750