drm/i915: don't clobber the special upscaling lvds timings

This regression has been introduced in

commit ca9bfa7e
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Sat Jan 28 14:49:20 2012 +0100

    drm/i915: fixup interlaced vertical timings confusion, part 1

Unfortunately that commit failed to take into account that the lvds
code does some special adjustements to the crtc timings for upscaling
an centering.

Fix this by explicitly computing crtc timings in the lvds mode fixup
function and setting a special flag in mode->private_flags if the crtc
timings have been adjusted.

v2: Add a comment to explain the new mode driver private flag,
suggested by Eugeni Dodonov.

v3: Kill the confusing and now redundant set_crtcinfo call in
intel_fixed_panel_mode, noticed by Chris Wilson.

Reported-and-Tested-by: Hans de Bruin <jmdebruin@xmsnet.nl>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=43071


Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>