drm/i915: Make skl_detach_scalers take crtc_state

Rename intel_crtc to crtc, and pass crtc_state instead of looking at
crtc->config.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181004094604.2646-6-maarten.lankhorst@linux.intel.com