replace fontrenderer.h include with forward declaration

in order to flatten the build dependency tree further, include
fontrenderer.h directly where needed, in header files a forward
declaration is enough

src/gui/scan_setup.cpp

@@ -51,6 +51,7 @@
 
 #include <driver/screen_max.h>
 #include <driver/framebuffer.h>
+#include <driver/fontrenderer.h>
 #include <driver/record.h>
 #include <system/debug.h>
 #include <system/helpers.h>