Enable custom backlight driver for kmac (#8397)

keyboards/kmac/rules.mk

@@ -27,7 +27,8 @@ CUSTOM_MATRIX = yes         # Custom matrix file
 SLEEP_LED_ENABLE = no       # Breathing sleep LED during USB suspend
 # if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
 NKRO_ENABLE = yes           # USB Nkey Rollover
-BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
+BACKLIGHT_ENABLE = yes      # Enable keyboard backlight functionality
+BACKLIGHT_DRIVER = custom
 MIDI_ENABLE = no            # MIDI support
 UNICODE_ENABLE = no         # Unicode
 BLUETOOTH_ENABLE = no       # Enable Bluetooth with the Adafruit EZ-Key HID