neutrino: explicitly include vfd/lcd header

Instead of including it everywhere through global.h, just include
the lcd/vfd header where needed. Add a tiny helper header "display.h"
to divert between vfd.h (coolstream) and lcdd.h (everything else).

src/gui/audiomute.cpp

@@ -32,6 +32,8 @@
 #include <gui/volumebar.h>
 #include <gui/audiomute.h>
 
+#include <driver/display.h>
+
 CAudioMute::CAudioMute()
 {
 	mute_ax		= 0;