drm/i915: Changes related to the sequence port no for

From now on for both DSI Ports A & C, the seq_port value has been
set to 0. seq_port value is parsed from Sequence block#53 of VBT.
So, for packets that needs to be read/write for DSI single link on
Port A and Port C will now be based on the DVO port from VBT block 2,
instead of seq_port.

Signed-off-by: Gaurav K Singh <gaurav.k.singh@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>