drm/i915/scaler: Convert the scaler code to intel_display

struct intel_display will replace struct drm_i915_private as
the main thing for display code. Convert the scaler code to
use it (as much as possible at this stage).

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241107122658.21901-6-ville.syrjala@linux.intel.com