drm/i915: Ensure that the crtcinfo is populated during mode_fixup()

This should fix the mysterious mode setting failures reported during
boot up and after resume, generally for i8xx class machines.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=16478


Reported-and-tested-by: Xavier Chantry <chantry.xavier@gmail.com>
Buzilla: https://bugs.freedesktop.org/show_bug.cgi?id=29413


Tested-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org