sched/core: Simplify helpers for rq clock update skip requests

By renaming the functions we can get rid of the skip parameter
and have better code redability. It makes zero sense to have
things such as:

  rq_clock_skip_update(rq, false)

When the skip request is in fact not going to happen. Ever. Rename
things such that we end up with:

  rq_clock_skip_update(rq)
  rq_clock_cancel_skipupdate(rq)

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Cc: matt@codeblueprint.co.uk
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/20180404161539.nhadkff2aats74jh@linux-n805


Signed-off-by: Ingo Molnar <mingo@kernel.org>