[Keyboard] Add S7 Elephant Rev2 Support (#9398)

* Add S7 Elephant Rev2 Support

* Apply suggestions from code review

I tested the changes on my board as well, thanks for the suggestions!

* Added a default folder in the makefile so that this would no longer be a breaking change

keyboards/s7_elephant/rules.mk

@@ -1,25 +1 @@
-# 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 = no    # Virtual DIP switch configuration
-MOUSEKEY_ENABLE = yes    # Mouse keys
-EXTRAKEY_ENABLE = yes    # Audio control and System control
-CONSOLE_ENABLE = no      # Console for debug
-COMMAND_ENABLE = no      # 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 = no    # Enable keyboard backlight functionality
-RGBLIGHT_ENABLE = yes    # Enable keyboard underlight functionality
+DEFAULT_FOLDER = s7_elephant/rev1