drm/i915: Eliminate crtc->config usage from CRT code

Replace crtc->config usage with the passed down crtc state.

Also take the opportunity for some s/pipe_config/crtc_state/ while at it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171031205123.13123-7-ville.syrjala@linux.intel.com
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>