ANDROID: add kernel/sched/android.h

Create a place for the android-specific scheduler addons to live so that
merges can happen easier and we have a better view of the technical debt
that is being drug along with the kernel updates.

Start it off with replacing an empty copy of task_may_not_preempt() to
solve the build problem for some devices where they are relying on this
function to be present in the system.

Fixes: 65c99af9 ("Revert "ANDROID: sched: avoid placing RT threads on cores handling softirqs"")
Cc: Quentin Perret <qperret@google.com>
Cc: Will McVicker <willmcvicker@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I4fd94fab3397b3a197b79b2ae27e9490b54cad59