drm/i915/dp: force eDP lane count to max available lanes on BDW

There are certain BDW high res eDP machines that regressed due to

commit 38aecea0
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Mon Mar 3 11:18:10 2014 +0100

    drm/i915: reverse dp link param selection, prefer fast over wide again

The commit lead to 2 lanes at 5.4 Gbps being used instead of 4 lanes at
2.7 Gbps on the affected machines. Link training succeeded for both, but
the screen remained blank with the former config. Further investigation
showed that 4 lanes at 5.4 Gbps worked also.

The root cause for the blank screen using 2 lanes remains unknown, but
apparently the driver for a certain other operating system by default
uses the max available lanes. Follow suit on Broadwell eDP, for at least
until we figure out what is going on.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76711


Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Tested-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>