drm/i915: Don't use crtc->config when reading out infoframe state

drm/i915: Don't use crtc->config when reading out infoframe state

The .get_config() hooks should not reference anything in crtc->config,
everything should be based on the passed in pipe_config instead. So
don't dig out the cpu_transcoder from crtc->config on ddi platfforms,
and also avoid using the encoder->crtc link and instead look up the
pipe via pipe_config->base.crtc.

I don't think this will actually fix anything since during the initial
state readout we set up the encoder->crtc link prior to calling
.get_config(), and during the modeset state check the encoder->crtc
ought to be correct anyway since it's that state we just programmed.
But this seems the right thing to do anyway.

While at it, do some house cleaning on the local variables in the
.infoframe_enabled() hooks.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448555227-31403-1-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>