ANDROID: fix 4.9 backport of psi header refactoring

The 4.9 backport of the patch https://lore.kernel.org/patchwork/patch/1052417/


introduced a build error when configured with CONFIG_CGROUP_SCHED disabled.
Functions threadgroup_change_begin and threadgroup_change_end were left
undefined. Fix this by moving them out of CONFIG_CGROUP_SCHED protection
the way they were defined initially.
Fixes: c405bfbb ("FROMLIST: refactor header includes to allow kthread.h inclusion in psi_types.h")

Bug: 127712811
Test: make allnoconfig
Change-Id: Ib6e2636fb4e0c47c885df4813082fae13b841cfe
Signed-off-by: Suren Baghdasaryan <surenb@google.com>