drm/i915: set CPT FDI RX polarity bits based on VBT

drm/i915: set CPT FDI RX polarity bits based on VBT

commit 3f704fa2778d3fe45e6529825a5c7a8bcbc686f4 upstream.

Check the VBT to see if the machine has inverted FDI RX polarity on
CPT. Based on this bit, set the appropriate bit on the TRANS_CHICKEN2
registers.

This should fix some machines that were showing black screens on all
outputs.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=60029
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>