x86/amd-iommu: attach devices to pre-allocated domains early

For some devices the ACPI table may define unity map
requirements which must me met when the IOMMU is enabled. So
we need to attach devices to their domains as early as
possible so that these mappings are in place when needed.
This patch assigns the domains right after they are
allocated. Otherwise this can result in I/O page faults
before a driver binds to a device and BIOS is still using
it.

Cc: stable@kernel.org
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>