x86, AMD IOMMU: replace DEVID macro with a function

This patch replaces the DEVID macro with a function and uses them where
apropriate (also in the core code).

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Cc: iommu@lists.linux-foundation.org
Cc: bhavna.sarathy@amd.com
Cc: robert.richter@amd.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>