dm: backlight: Add a backlight uclass

LCD panels normally have a backlight which can be controlled to illuminate
the LCD contents. Add a uclass to support this. Initially it only has a
method to enable the backlight.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/backlight.h

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2016 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _BACKLIGHT_H
+#define _BACKLIGHT_H
+
+struct backlight_ops {
+	/**
+	 * enable() - Enable a backlight
+	 *
+	 * @dev:	Backlight device to enable
+	 * @return 0 if OK, -ve on error
+	 */
+	int (*enable)(struct udevice *dev);
+};
+
+#define backlight_get_ops(dev)	((struct backlight_ops *)(dev)->driver->ops)
+
+/**
+ * backlight_enable() - Enable a backlight
+ *
+ * @dev:	Backlight device to enable
+ * @return 0 if OK, -ve on error
+ */
+int backlight_enable(struct udevice *dev);
+
+#endif