sched/core: Clean up kernel/sched/sched.h a bit

 - Fix whitespace noise
 - Fix col80 linebreak damage where possible
 - Apply CodingStyle consistently
 - Use consistent #else and #endif comments
 - Use consistent vertical alignment
 - Use 'extern' consistently

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