drm/i915: Clean up skl+ PLANE_POS vs. scaler handling

On skl+ the scaler (when enabled) will take care of the plane output
position. Make the code less ugly by just setting crtc_x/y to 0
when the scaler is enabled.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181101150605.18235-6-ville.syrjala@linux.intel.com


Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>