sched/headers: Reorganize, clean up and optimize kernel/sched/build_utility.c dependencies

Use all generic headers from kernel/sched/sched.h that are required
for it to build.

Sort the sections alphabetically.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Peter Zijlstra <peterz@infradead.org>