drm/i915: Use cpu_transcoder for HSW_TVIDEO_DIP_* instead of pipe

While old platforms had 3 transcoders and 3 pipes (1:1), HSW has
4 transcoders and 3 pipes.
These regs were being used only by HDMI code where pipe is always the same
thing as cpu_transcoder.
This patch allow us to use them for DP, specially for TRANSCODER_EDP.

v2: Adding HSW_TVIDEO_DIP_VSC_DATA to transmit vsc to eDP.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>