context_tracking, rcu: Rename rcu_dynticks_task*() into rcu_task*()

The context_tracking.state RCU_DYNTICKS subvariable has been renamed to
RCU_WATCHING, and the 'dynticks' prefix can be dropped without losing any
meaning.

While at it, flip the suffixes of these helpers. We are not telling
that we are entering dynticks mode from an RCU-task perspective anymore; we
are telling that we are exiting RCU-tasks because we are in eqs mode.

[ neeraj.upadhyay: Incorporate Frederic Weisbecker feedback. ]

Suggested-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>