drm/i915/bios: Clamp VBT HDMI level shift on BDW

Apparently some BDW machines (eg. HP Pavilion 15-ab) shipped with
a VBT inherited from some earlier HSW model. On HSW the HDMI level
shift value could go up to 11, whereas on BDW the maximum value is
9.

The DDI code does clamp the bogus value, but it does so with
a WARN which we don't really want. To avoid that let's just sanitize
the bogus VBT HDMI level shift value ahead of time for all BDW machines.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/9461


Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231013140214.1713-1-ville.syrjala@linux.intel.com


Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>