ioat2: catch and recover from broken vtd configurations v6

ioat2: catch and recover from broken vtd configurations v6

On some platforms (MacPro3,1) the BIOS assigns the ioatdma device to the
incorrect iommu causing faults when the driver initializes.  Add a quirk
to catch this misconfiguration and try falling back to untranslated
operation (which works in the MacPro3,1 case).

Assuming there are other platforms with misconfigured iommus teach the
ioatdma driver to treat initialization failures as non-fatal (just fail
the driver load and emit a warning instead of triggering a BUG_ON).

This can be classified as a boot regression since 2.6.32 on affected
platforms since the ioatdma module did not autoload prior to that
kernel.

Cc: <stable@kernel.org>
Acked-by: David Woodhouse <David.Woodhouse@intel.com>
Reported-by: Chris Li <lkml@chrisli.org>
Tested-by: Chris Li <lkml@chrisli.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>