drm/i915: Calculate haswell plane workaround, v5.

drm/i915: Calculate haswell plane workaround, v5.

This needs to be done last after all modesets have been calculated.

A modeset first disables all crtc's, so any crtc that undergoes a
modeset counts as inactive.

If no modeset's done, or > 1 crtc's stay w/a doesn't apply.
Apply workaround on the first crtc if 1 crtc stays active.
Apply workaround on the second crtc if no crtc was active.

Changes since v1:
 - Use intel_crtc->atomic as a place to put hsw_workaround_pipe.
 - Make sure quirk only applies to haswell.
 - Use first loop to iterate over newly enabled crtc's only.
   This increases readability.
Changes since v2:
 - Move hsw_workaround_pipe back to crtc_state.
Changes since v3:
 - Return errors from haswell_mode_set_planes_workaround.
Changes since v4:
- Clean up commit message.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>