iommu/vt-d: Move deferred device attachment into helper function

iommu/vt-d: Move deferred device attachment into helper function

BugLink: https://bugs.launchpad.net/bugs/1922738
Move the code that does the deferred device attachment into a separate
helper function.

Fixes: 1ee0186b9a12 ("iommu/vt-d: Refactor find_domain() helper")
Cc: stable@vger.kernel.org # v5.5
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
(cherry picked from commit 034d98cc0cdcde2415c6f598fa9125e3eaa02569)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>