DisplayLink UDL driver with Intel IOMMU enabled

[Volker Vogelhuber]

I just came across a DMAR allocation issue when I wanted to use the UDL 
driver with a DL-165 chipset and had the Intel IOMMU enabled.

It seems like it could be solved with the same patch already applied to 
the EVDI driver: 
https://github.com/DisplayLink/evdi/commit/74e289906dba95c0ad3208cfa6a57ba3042b930f

So just add interface->dev.archdata.iommu = INTEL_IOMMU_DUMMY_DOMAIN;
before the drm_dev_alloc call in udl_drv.c seems to be enough to use
the UDL driver with IOMMU enabled.

Kind regards,
    Volker