x86/amd-iommu: Use get_device_id and check_device where appropriate

The logic of these two functions is reimplemented (at least
in parts) in places in the code. This patch removes these
code duplications and uses the functions instead. As a side
effect it moves check_device() to the helper function code
section.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>