apple_bl: Add register/unregister functions

Add functions to allow other modules to enable or disable apple_bl. This
will be used by the gmux driver to disable apple_bl when the gmux is
present, as it is a better and more reliable option for brightness
control.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>
diff --git a/include/linux/apple_bl.h b/include/linux/apple_bl.h
new file mode 100644
index 0000000..47bedc0
--- /dev/null
+++ b/include/linux/apple_bl.h
@@ -0,0 +1,26 @@
+/*
+ * apple_bl exported symbols
+ */
+
+#ifndef _LINUX_APPLE_BL_H
+#define _LINUX_APPLE_BL_H
+
+#ifdef CONFIG_BACKLIGHT_APPLE
+
+extern int apple_bl_register(void);
+extern void apple_bl_unregister(void);
+
+#else /* !CONFIG_BACKLIGHT_APPLE */
+
+static inline int apple_bl_register(void)
+{
+	return 0;
+}
+
+static inline void apple_bl_unregister(void)
+{
+}
+
+#endif /* !CONFIG_BACKLIGHT_APPLE */
+
+#endif /* _LINUX_APPLE_BL_H */