[Keyboard] Adds Elongate Revision Delta PCB support (#15498)

Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: James Young <18669334+noroadsleft@users.noreply.github.com>
Co-authored-by: Ryan <fauxpark@gmail.com>

keyboards/acheron/elongate/delta/rules.mk

@@ -0,0 +1,20 @@
+# 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
+NKRO_ENABLE = yes           # Enable N-Key Rollover
+BACKLIGHT_ENABLE = yes      # Enable keyboard backlight functionality
+RGBLIGHT_ENABLE = yes       # 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