drm/i915: Eliminate some encoder->crtc usage from TV code

Extract the current crtc from the crtc state rather than via
the legacy encoder->crtc pointer whenever possible.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171031205123.13123-5-ville.syrjala@linux.intel.com


Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>