XD68 Configurator Layout Support and Minor Refactor (#7904)

* XD68: QMK Configurator layout support

* elevate backlight breathing settings to keyboard level

* remove empty keymap config.h files

* rules.mk templating

* keymap polishing

- four-space indent
- keycode alignment

keyboards/xd68/config.h

@@ -50,6 +50,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #define BACKLIGHT_PIN F5
 #define BACKLIGHT_LEVELS 6
+#define BACKLIGHT_BREATHING
+#define BREATHING_PERIOD 6
 
 /* Debounce reduces chatter (unintended double-presses) - set 0 if debouncing is not needed */
 #define DEBOUNCE 5