sched/deadline: Fix accounting after global limits change

A global limits change (sched_rt_handler() logic) currently leaves stale
and/or incorrect values in variables related to accounting (e.g.
extra_bw).

Properly clean up per runqueue variables before implementing the change
and rebuild scheduling domains (so that accounting is also properly
restored) after such a change is complete.

Reported-by: Marcel Ziswiler <marcel.ziswiler@codethink.co.uk>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Marcel Ziswiler <marcel.ziswiler@codethink.co.uk> # nuc & rock5b
Link: https://lore.kernel.org/r/20250627115118.438797-4-juri.lelli@redhat.com