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/Marlin_main.cpp

@@ -279,6 +279,10 @@
   #include "watchdog.h"
 #endif
 
+#if ENABLED(MAX7219_DEBUG)
+  #include "Max7219_Debug_LEDs.h"
+#endif
+
 #if ENABLED(NEOPIXEL_RGBW_LED)
   #include <Adafruit_NeoPixel.h>
 #endif
@@ -10292,7 +10296,7 @@ inline void invalid_extruder_error(const uint8_t e) {
       SET_OUTPUT(FANMUX1_PIN);
       #if PIN_EXISTS(FANMUX2)
         SET_OUTPUT(FANMUX2_PIN);
-      #endif 
+      #endif
     #endif
     fanmux_switch(0);
   }
@@ -13201,6 +13205,10 @@ void idle(
     bool no_stepper_sleep/*=false*/
   #endif
 ) {
+  #if ENABLED(MAX7219_DEBUG)
+    Max7219_idle_tasks();
+  #endif  // MAX7219_DEBUG
+
   lcd_update();
 
   host_keepalive();
@@ -13316,6 +13324,10 @@ void stop() {
  */
 void setup() {
 
+  #if ENABLED(MAX7219_DEBUG)
+    Max7219_init();
+  #endif
+
   #ifdef DISABLE_JTAG
     // Disable JTAG on AT90USB chips to free up pins for IO
     MCUCR = 0x80;
@@ -13467,11 +13479,11 @@ void setup() {
     SET_OUTPUT(E_MUX1_PIN);
     SET_OUTPUT(E_MUX2_PIN);
   #endif
-  
+
   #if HAS_FANMUX
     fanmux_init();
   #endif
-  
+
   lcd_init();
 
   #ifndef CUSTOM_BOOTSCREEN_TIMEOUT