Enable backlight breathing support for the TADA68 (#9145)

The factory TMK firmware for the TADA68 supports backlight breathing,
so I was surprised when the BL_BRTG key I set up in the online QMK
configurator didn't work.

As far as I can tell, this was just a simple omission.

keyboards/tada68/config.h

@@ -37,8 +37,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define MATRIX_COL_PINS {F0,F1,E6,C7,C6,B7,D4,B1,B0,B5,B4,D7,D6,B3,F4}
 #define UNUSED_PINS
 
-#define BACKLIGHT_PIN B6
-
 /* COL2ROW or ROW2COL */
 #define DIODE_DIRECTION COL2ROW
 
@@ -53,8 +51,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 /* Locking resynchronize hack */
 #define LOCKING_RESYNC_ENABLE
 
-/* Backlight configuration
- */
+/* Backlight configuration */
+#define BACKLIGHT_PIN B6
+#define BACKLIGHT_BREATHING
 #define BACKLIGHT_LEVELS 4
 
 /*