ANDROID: sched: move blocked reason trace point to cover all class

Now, we only export CFS taks' blocked reasons but it's
important and useful to know other class' blocked
reasons such as RT tasks.

Move the blocked reason trace point to where the scheduler
core layer and before the task's state moves to the waking
state. Thus, we could cover all the sched classes.

Bug: 203080186
Test: check traces
Signed-off-by: Martin Liu <liumartin@google.com>
Change-Id: Ic61865642d852d0127cdcf474adf8c06e4c2d570