drm/i915/display: add intel_display_device_present()

drm/i915/display: add intel_display_device_present()

Add a proper function for display && HAS_DISPLAY(display) to hide
indirect struct intel_display access via the macro from a number of
places outside of display. This makes struct intel_display * an opaque
pointer in these places. All HAS_DISPLAY() usage is now constrained
within display.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/20250903090408.3492875-1-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>