intel-iommu: Detect DMAR in hyperspace at probe time.

intel-iommu: Detect DMAR in hyperspace at probe time.

commit 2c99220810c1c79322034628b993573b088ff2da upstream.

Many BIOSes will lie to us about the existence of an IOMMU, and claim
that there is one at an address which actually returns all 0xFF.

We need to detect this early, so that we know we don't have a viable
IOMMU and can set up swiotlb before it's too late.

Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>