Move tmk_core/common/backlight to quantum/backlight (#6710)

* Move tmk_core/common/backlight to quantum/backlight

* Add guards to backlight inclusion

* Add guards to backlight inclusion

* Update backlight guards on clueboard/60

* Use full paths to avoid vpath issues

tmk_core/common/avr/suspend.c

@@ -4,7 +4,6 @@
 #include <avr/interrupt.h>
 #include "matrix.h"
 #include "action.h"
-#include "backlight.h"
 #include "suspend_avr.h"
 #include "suspend.h"
 #include "timer.h"
@@ -16,6 +15,10 @@
 #    include "lufa.h"
 #endif
 
+#ifdef BACKLIGHT_ENABLE
+#    include "backlight.h"
+#endif
+
 #ifdef AUDIO_ENABLE
 #    include "audio.h"
 #endif /* AUDIO_ENABLE */