rcu: Rename rcu_dynticks_in_eqs() into rcu_watching_snap_in_eqs()

The context_tracking.state RCU_DYNTICKS subvariable has been renamed to
RCU_WATCHING, reflect that change in the related helpers.

While at it, update a comment that still refers to rcu_dynticks_snap(),
which was removed by commit:

  7be2e6323b9b ("rcu: Remove full memory barrier on RCU stall printout")

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