drm/i915/sdvo: Include LVDS panels for the IS_DIGITAL check

We were checking whether the supplied edid matched the connector it was
read from. We do this in case a DDC read returns an EDID for another
device on a multifunction or otherwise interesting card. However, we
failed to include LVDS as a digital device and so rejecting an otherwise
valid EDID.

Fixes the detection of the secondary SDVO LVDS panel on the Libretto
W105.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=39216
Signed-off-by: Keith Packard <keithp@keithp.com>