drm/i915/tc: Update DP_MODE programming

BSpec was updated(r146548) with a new MG_DP_MODE Programming table,
now taking in consideration the pin assignment and allowing us to
optimize power by shutting down available but not needed lanes.

It was tested on ICL and TGL, with adaptors that used pin assignment
C and B, reversing the connector and going to different modes testing
the not needed lane shutdown.

v5:
Using crtc_state->lane_count instead of dp.lane_count

BSpec: 21735
BSpec: 49292

Cc: Imre Deak <imre.deak@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Clinton A Taylor <clinton.a.taylor@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190926210659.56317-1-jose.souza@intel.com