drm/i915: Use intel_de_write_fw() for skl+ scaler registers

We have to write quite a few registers when programming the
pipe scaler. Let's use intel_de_write_fw() for these to reduce
the lockdep overhead a bit. All plane registers (including plane
scaler) already do this.

We already had a few accidental intel_de_write_fw() in there.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200212161738.28141-3-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>