iommu/vt-d: Gracefully handle DMAR units with no supported address widths

iommu/vt-d: Gracefully handle DMAR units with no supported address widths

Instead of bailing out completely, such a unit can still be used for
interrupt remapping.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/linux-iommu/549928db2de6532117f36c9c810373c14cf76f51.camel@infradead.org/
Signed-off-by: Joerg Roedel <jroedel@suse.de>
(cherry picked from commit c40aaaac1018ff1382f2d35df5129a6bcea3df6b and
 subsequent build fix commit 9def3b1a07c41e21c68a0eb353e3e569fdd1d2b1)