context_tracking, rcu: Rename DYNTICK_IRQ_NONIDLE into CT_NESTING_IRQ_NONIDLE

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

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