sched: Rename ttwu_post_activation() to ttwu_do_wakeup()

The ttwu_post_activation() code does the core wakeup, it sets TASK_RUNNING
and performs wakeup-preemption, so give is a more descriptive name.

Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110405152729.434609705@chello.nl