[Keyboard] Add Sauce Mild Keyboard (#14287)

Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Ryan <fauxpark@gmail.com>

keyboards/sauce/mild/rules.mk

@@ -0,0 +1,24 @@
+# MCU name
+MCU = STM32F072
+
+# 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 = no         # Console for debug
+COMMAND_ENABLE = no         # Commands for debug and configuration
+# Do not enable SLEEP_LED_ENABLE. it uses the same timer as BACKLIGHT_ENABLE
+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
+RGBLIGHT_ENABLE = no        # Enable keyboard RGB underglow
+AUDIO_ENABLE = no           # Audio output
+
+# Enter lower-power sleep mode when on the ChibiOS idle thread
+OPT_DEFS += -DCORTEX_ENABLE_WFI_IDLE=TRUE