boards: Convert nucleo_c031c6 to HWM v2

Port the board to HWMv2.

Signed-off-by: Guillaume Gautier <guillaume.gautier-ext@st.com>

boards/boards_legacy/arm/nucleo_c031c6/Kconfig.board

@@ -1,8 +0,0 @@
-# STM32 Nucleo-64 development board with STM32C031C6 MCU configuration
-
-# Copyright (c) 2023 Benjamin Björnsson <benjamin.bjornsson@gmail.com>
-# SPDX-License-Identifier: Apache-2.0
-
-config BOARD_NUCLEO_C031C6
-	bool "NUCLEO-64 C031C6 Development Board"
-	depends on SOC_STM32C031XX

boards/boards_legacy/arm/nucleo_c031c6/Kconfig.defconfig

@@ -1,11 +0,0 @@
-# STM32 Nucleo-64 development board with STM32C031C6 MCU
-
-# Copyright (c) 2023 Benjamin Björnsson <benjamin.bjornsson@gmail.com>
-# SPDX-License-Identifier: Apache-2.0
-
-if BOARD_NUCLEO_C031C6
-
-config BOARD
-	default "nucleo_c031c6"
-
-endif # BOARD_NUCLEO_C031C6

boards/st/nucleo_c031c6/Kconfig.nucleo_c031c6

@@ -0,0 +1,5 @@
+# Copyright (c) 2023 Benjamin Björnsson <benjamin.bjornsson@gmail.com>
+# SPDX-License-Identifier: Apache-2.0
+
+config BOARD_NUCLEO_C031C6
+	select SOC_STM32C031XX

boards/st/nucleo_c031c6/board.yml

@@ -0,0 +1,5 @@
+board:
+  name: nucleo_c031c6
+  vendor: st
+  socs:
+    - name: stm32c031xx

boards/st/nucleo_c031c6/nucleo_c031c6_defconfig

@@ -1,11 +1,5 @@
 # SPDX-License-Identifier: Apache-2.0
 
-# Zephyr Kernel Configuration
-CONFIG_SOC_SERIES_STM32C0X=y
-
-# Platform Configuration
-CONFIG_SOC_STM32C031XX=y
-
 # Serial Drivers
 CONFIG_SERIAL=y
 CONFIG_UART_INTERRUPT_DRIVEN=y