drm/i915/xelpd: Required bandwidth increases when VT-d is active

If VT-d is active, the memory bandwidth usage of the display is 5%
higher.  Take this into account when determining whether we can support
a display configuration.

Bspec: 64631
Cc: Matt Atwood <matthew.s.atwood@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210512042144.2089071-5-matthew.d.roper@intel.com