[Keyboard] Add ymd67 keyboard (#7631)

* [Keyboard] Add ymd67 keyboard

* Apply suggestions from code review

* Apply more suggestions from code review

keyboards/ymdk/ymd67/rules.mk

@@ -0,0 +1,26 @@
+# MCU name
+MCU = atmega32u4
+
+# Bootloader selection
+#   Teensy       halfkay
+#   Pro Micro    caterina
+#   Atmel DFU    atmel-dfu
+#   LUFA DFU     lufa-dfu
+#   QMK DFU      qmk-dfu
+#   ATmega32A    bootloadHID
+#   ATmega328P   USBasp
+BOOTLOADER = atmel-dfu
+
+# Build Options
+#   comment out to disable the options.
+#
+BOOTMAGIC_ENABLE = yes # Virtual DIP switch configuration
+MOUSEKEY_ENABLE = no   # Mouse keys
+EXTRAKEY_ENABLE = yes  # Audio control and System control
+CONSOLE_ENABLE = no    # Console for debug
+COMMAND_ENABLE = yes   # Commands for debug and configuration
+SLEEP_LED_ENABLE = no  # Breathing sleep LED during USB suspend
+NKRO_ENABLE = yes      # USB Nkey Rollover - if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
+BACKLIGHT_ENABLE = yes # Enable keyboard backlight functionality
+AUDIO_ENABLE = no
+RGBLIGHT_ENABLE = yes