Relocate magic keycode processing (#7512)

* Move magic keycode processing to own file

* Save some bytes

* Update comments

* Update define to one thats not already used...

* Fix audio

quantum/quantum.h

@@ -133,6 +133,10 @@ extern layer_state_t layer_state;
 #    include "process_space_cadet.h"
 #endif
 
+#ifdef MAGIC_KEYCODE_ENABLE
+#    include "process_magic.h"
+#endif
+
 #ifdef HD44780_ENABLE
 #    include "hd44780.h"
 #endif