fbdev/sbus: Forward declare all necessary structures in header

In sbuslib.h, declare all of the header file's structs at the
top. No functional changes.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230806120926.5368-3-tzimmermann@suse.de

drivers/video/fbdev/sbuslib.h

@@ -3,6 +3,11 @@
 #ifndef _SBUSLIB_H
 #define _SBUSLIB_H
 
+struct device_node;
+struct fb_info;
+struct fb_var_screeninfo;
+struct vm_area_struct;
+
 struct sbus_mmap_map {
 	unsigned long voff;
 	unsigned long poff;
@@ -14,7 +19,6 @@ struct sbus_mmap_map {
 
 extern void sbusfb_fill_var(struct fb_var_screeninfo *var,
 			    struct device_node *dp, int bpp);
-struct vm_area_struct;
 extern int sbusfb_mmap_helper(struct sbus_mmap_map *map,
 			      unsigned long physbase, unsigned long fbsize,
 			      unsigned long iospace,