The fast path will soon need to find an ITS by doorbell address, as the
translation caches will become local to an ITS. Spin off a helper to do
just that.
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240422200158.2606761-10-oliver.upton@linux.devSigned-off-by: Marc Zyngier <maz@kernel.org>