intel-iommu: Check for 'DMAR at zero' BIOS error earlier.
Chris Wright has some patches which let us fall back to swiotlb nicely if IOMMU initialisation fails. But those are a bit much for 2.6.32. Instead, let's shift the check for the biggest problem, the HP and Acer BIOS bug which reports a DMAR at physical address zero. That one can actually be checked much earlier -- before we even admit to having detected an IOMMU in the first place. So the swiotlb init goes ahead as we want. Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>