fbdev: Do not include <linux/notifier.h> in header

Forward declare struct notifier_block and remove the include
statement.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240219093941.3684-7-tzimmermann@suse.de

include/linux/fb.h

@@ -10,7 +10,6 @@
 
 #include <linux/init.h>
 #include <linux/workqueue.h>
-#include <linux/notifier.h>
 #include <linux/list.h>
 #include <linux/slab.h>
 
@@ -22,6 +21,7 @@ struct fb_info;
 struct device;
 struct file;
 struct inode;
+struct notifier_block;
 struct videomode;
 struct device_node;