VT-d: don't reject valid DMAR/ATSR tables on systems with multiple PCI segments

VT-d: don't reject valid DMAR/ATSR tables on systems with multiple PCI segments

On multi-PCI-segment systems, each segment has to be expected to have
an include-all DRHD and an all-ports ATSR, so the firmware consistency
check incorrectly rejects valid configurations there (which is
particularly problematic when the firmware also pre-enabled x2apic
mode, as the system will panic in that case due to being unable to
enable interrupt remapping). Thus constrain the check to just segment
0 for now; once full multi-segment support is there (which I'm working
on), it can be revisited whether we'd want to track this per segment,
or whether we trust the firmware of such large systems.

Signed-off-by: Jan Beulich <jbeulich@novell.com>