Add Max7219 LED Matrix Debug Support (#7563)

* Add Max7219 LED Matrix Debug Support

The Max7219 8x8 LED Matrix's are very helpful for debugging new code.
And for that matter, just trying to maximize printer settings without
causing stuttering.

The displays are very inexpensive (under $2.00 with shipping) and
provide a lot of help when trying to debug complicated code.

* Try to keep Makefile up to date.

Marlin/Makefile

@@ -310,7 +310,7 @@ CXXSRC = WMath.cpp WString.cpp Print.cpp Marlin_main.cpp \
 	temperature.cpp cardreader.cpp configuration_store.cpp \
 	watchdog.cpp SPI.cpp servo.cpp Tone.cpp ultralcd.cpp digipot_mcp4451.cpp \
 	dac_mcp4728.cpp vector_3.cpp least_squares_fit.cpp endstops.cpp stopwatch.cpp utility.cpp \
-	printcounter.cpp nozzle.cpp serial.cpp gcode.cpp
+	printcounter.cpp nozzle.cpp serial.cpp gcode.cpp Max7219_Debug_LEDs.cpp
 ifeq ($(NEOPIXEL), 1)
 CXXSRC += Adafruit_NeoPixel.cpp
 endif