[Keyboard] Add XS108 (#19112)

Co-authored-by: Ryan <fauxpark@gmail.com>

keyboards/xelus/xs108/rules.mk

@@ -0,0 +1,22 @@
+# MCU name
+MCU = STM32L412
+
+# Bootloader selection
+BOOTLOADER = stm32-dfu
+
+# Build Options
+#   change yes to no to disable
+#
+BOOTMAGIC_ENABLE = yes      # Enable Bootmagic Lite
+MOUSEKEY_ENABLE = yes       # Mouse keys
+EXTRAKEY_ENABLE = yes       # Audio control and System control
+CONSOLE_ENABLE = yes        # Console for debug
+COMMAND_ENABLE = yes        # Commands for debug and configuration
+NKRO_ENABLE = yes           # Enable N-Key Rollover
+BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
+RGBLIGHT_ENABLE = no        # Enable keyboard RGB underglow
+AUDIO_ENABLE = no           # Audio output
+EEPROM_DRIVER = i2c
+
+# Enter lower-power sleep mode when on the ChibiOS idle thread
+OPT_DEFS += -DCORTEX_ENABLE_WFI_IDLE=TRUE