drm/i915/display: support struct intel_atomic_state in to_intel_display()

Add support for converting struct intel_atomic_state pointers to struct
intel_display pointers.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240813164123.2674462-1-jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>