VT-d: fix iommu=no-igfx if the IOMMU scope contains fake device(s)

VT-d: fix iommu=no-igfx if the IOMMU scope contains fake device(s)

If the scope for IGD's IOMMU contains additional device that doesn't
actually exist, iommu=no-igfx would not disable that IOMMU. In this
particular case (Thinkpad x230) it included 00:02.1, but there is no
such device on this platform. Consider only existing devices for the
"gfx only" check as well as the establishing of IGD DRHD address
(underlying is_igd_drhd(), which is used to determine applicability of
two workarounds).

Fixes: 2d7f191b392e ("VT-d: generalize and correct "iommu=no-igfx" handling")
Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
master commit: 49de6749baa8d0addc3048defd4ef3e85cb135e9
master date: 2023-03-23 09:16:41 +0100