Add elephant42 keyboard (#14336)

keyboards/elephant42/rules.mk

@@ -0,0 +1,23 @@
+# MCU name
+MCU = atmega32u4
+
+# Bootloader selection
+BOOTLOADER = caterina
+
+# Build Options
+#   change yes to no to disable
+#
+BOOTMAGIC_ENABLE = yes      # Enable Bootmagic Lite
+MOUSEKEY_ENABLE = no       # Mouse keys
+EXTRAKEY_ENABLE = yes       # Audio control and System control
+CONSOLE_ENABLE = no         # Console for debug
+COMMAND_ENABLE = no         # Commands for debug and configuration
+NKRO_ENABLE = no            # Enable N-Key Rollover
+BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
+RGBLIGHT_ENABLE = no        # Enable keyboard RGB underglow
+RGB_MATRIX_ENABLE = yes
+RGB_MATRIX_DRIVER = WS2812
+AUDIO_ENABLE = no           # Audio output
+SPLIT_KEYBOARD = yes
+OLED_ENABLE = yes
+LTO_ENABLE = yes