feedbackd: Support visual feedback via LEDs

Currently all LED feedbacks are infinite we can improve that
later on by using the 'repeat' attribute of the LED pattern
trigger.

src/fbd-udev.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright (C) 2020 Purism SPC
+ *
+ * SPDX-License-Identifier: GPL-3.0+
+ */
+#pragma once
+
+#include <glib.h>
+#include <gudev/gudev.h>
+
+
+G_BEGIN_DECLS
+
+gboolean fbd_udev_set_sysfs_path_attr_as_string (GUdevDevice *dev, const gchar *attr,
+						 const gchar *s, GError **err);
+gboolean fbd_udev_set_sysfs_path_attr_as_int (GUdevDevice *dev, const gchar *attr,
+					      gint val, GError **err);
+
+G_END_DECLS