Due to recurring issues with DMAR support on certain platforms.
There's a number of filesystem corruption incidents reported:

  https://bugzilla.redhat.com/show_bug.cgi?id=479996
  http://bugzilla.kernel.org/show_bug.cgi?id=12578

Provide a Kconfig option to change whether it is enabled by
default.

If disabled, it can still be reenabled by passing intel_iommu=on to the
kernel. Keep the .config option off by default.
Signed-off-by: NKyle McMartin <kyle@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Acked-By: NDavid Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>