drm/i915: Guard debugfs against invalid access without display

Do not create the display debugfs files when we don't have display.

Based on previous patch by José Souza.

Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201027044618.719064-1-lucas.demarchi@intel.com

drivers/gpu/drm/i915/i915_drv.c

@@ -671,7 +671,8 @@ static void i915_driver_register(struct drm_i915_private *dev_priv)
 	/* Reveal our presence to userspace */
 	if (drm_dev_register(dev, 0) == 0) {
 		i915_debugfs_register(dev_priv);
-		intel_display_debugfs_register(dev_priv);
+		if (HAS_DISPLAY(dev_priv))
+			intel_display_debugfs_register(dev_priv);
 		i915_setup_sysfs(dev_priv);
 
 		/* Depends on sysfs having been initialized */