sched/deadline: Use ENQUEUE_MOVE to allow priority change

Pierre reported hitting balance callback warnings for deadline tasks
after commit 6455ad53 ("sched: Move sched_class::prio_changed()
into the change pattern").

It turns out that DEQUEUE_SAVE+ENQUEUE_RESTORE does not preserve DL
priority and subsequently trips a balance pass -- where one was not
expected.

From discussion with Juri and Luca, the purpose of this clause was to
deal with tasks new to DL and all those sites will have MOVE set (as
well as CLASS, but MOVE is move conservative at this point).

Per the previous patches MOVE is audited to always run the balance
callbacks, so switch enqueue_dl_entity() to use MOVE for this case.

Fixes: 6455ad53 ("sched: Move sched_class::prio_changed() into the change pattern")
Reported-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Pierre Gondois <pierre.gondois@arm.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://patch.msgid.link/20260114130528.GB831285@noisy.programming.kicks-ass.net