drm/i915: Finish intel_sprite.c struct intel_display conversion

drm/i915: Finish intel_sprite.c struct intel_display conversion

intel_sprite.c was partially converted to struct intel_display.
Finish the job now that we can deal with the platform checks
as well.

And while at it we also move the 'display' variable declaration
to be the first thing in most functions, consistency. We can
actually do that now since intel_display() accepts the intel_plane
and intel_plane_state types.

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/20250206185533.32306-9-ville.syrjala@linux.intel.com