drm/i915: Stop using crtc->index as the pipe

drm/i915: Stop using crtc->index as the pipe

The pipe crc code slipped theough the net when we tried to
eliminate all crtc->index==pipe abuses. Remedy that.

And while at it get rid of those nasty intel_crtc+drm_crtc
pointer aliases.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210426185612.13223-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>