drm/i915: move cpu_transcoder to the pipe configuration

For a bunch of reason we need to more accurately track this:
- hw pipe state readout for Haswell needs the cpu transcoder.
- We need to know the right cpu transcoder in a bunch of places in
  ->disable and other modeset callbacks.

In the future we need to add hw state readout&check support, too. But
to avoid ugly merge conflicts do the rote sed job now without any
functional changes.

v2: Preserve the cpu_transcoder value when overwriting crtc->config.
Reported by Paulo.

Cc: Paulo Zanoni <przanoni@gmail.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v1)
[danvet: Removed rough whitespace that Chris spotted.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>