iommu/intel: disable DMAR for g4x integrated gfx

DMAR support on g4x/gm45 integrated gpus seems to be totally busted.
So don't bother, but instead disable it by default to allow distros to
unconditionally enable DMAR support.

v2: Actually wire up the right quirk entry, spotted by Adam Jackson.

Note that according to intel marketing materials only g45 and gm45
support DMAR/VT-d. So we have reports for all relevant gen4 pci ids by
now. Still, keep all the other gen4 ids in the quirk table in case the
marketing stuff confused me again, which would not be the first time.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=51921
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=538163
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=538163
Cc: Adam Jackson <ajax@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: stable@vger.kernel.org
Acked-By: David Woodhouse <David.Woodhouse@intel.com>
Tested-by: stathis <stathis@npcglib.org>
Tested-by: Mihai Moldovan <ionic@ionic.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>