drm/i915: Allow DSI dual link to be configured on any pipe

drm/i915: Allow DSI dual link to be configured on any pipe

Just like single link MIPI panels, similarly for dual link panels, pipe
to be configured is based on the DVO port from VBT Block 2. In hardware,
Port A is mapped with Pipe A and Port C is mapped with Pipe B.

This issue got introduced in -

commit 53c59f5ee6dd3580f7595369797f97ed3530ae25
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Fri Jan 16 14:27:23 2015 +0200

    drm/i915/dsi: add drm mipi dsi host support

Cc: stable@vger.kernel.org # v4.0
Signed-off-by: Gaurav K Singh <gaurav.k.singh@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>