boards: Convert nucleo_l031k6 to HWM v2

Port the board to HWMv2.

Signed-off-by: Erwan Gouriou <erwan.gouriou@st.com>

boards/boards_legacy/arm/nucleo_l031k6/Kconfig.board

@@ -1,8 +0,0 @@
-# STM32 Nucleo-32 development board with STM32L031K6 MCU configuration
-
-# Copyright (c) 2020 Steven Daglish <s.c.daglish@gmail.com>
-# SPDX-License-Identifier: Apache-2.0
-
-config BOARD_NUCLEO_L031K6
-	bool "NUCLEO-32 L031K6 Development Board"
-	depends on SOC_STM32L031XX

boards/st/nucleo_l031k6/Kconfig.defconfig

@@ -5,9 +5,6 @@
 
 if BOARD_NUCLEO_L031K6
 
-config BOARD
-	default "nucleo_l031k6"
-
 config SPI_STM32_INTERRUPT
 	default y
 	depends on SPI

boards/st/nucleo_l031k6/Kconfig.nucleo_l031k6

@@ -0,0 +1,5 @@
+# Copyright (c) 2020 Steven Daglish <s.c.daglish@gmail.com>
+# SPDX-License-Identifier: Apache-2.0
+
+config BOARD_NUCLEO_L031K6
+	select SOC_STM32L031XX

boards/st/nucleo_l031k6/board.yml

@@ -0,0 +1,5 @@
+board:
+  name: nucleo_l031k6
+  vendor: st
+  socs:
+    - name: stm32l031xx

boards/st/nucleo_l031k6/doc/index.rst

@@ -88,7 +88,7 @@ The Zephyr nucleo_l031k6 board configuration supports the following hardware fea
 Other hardware features are not yet supported in this Zephyr port.
 
 The default configuration can be found in the defconfig file:
-``boards/arm/nucleo_l031k6/nucleo_l031k6_defconfig``
+:zephyr_file:`boards/st/nucleo_l031k6/nucleo_l031k6_defconfig`
 
 Connections and IOs
 ===================

boards/st/nucleo_l031k6/nucleo_l031k6_defconfig

@@ -1,11 +1,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 # Zephyr Kernel Configuration
-CONFIG_SOC_SERIES_STM32L0X=y
-
 # Platform Configuration
-CONFIG_SOC_STM32L031XX=y
-
 # Kernel Options due to Low Memory (8k)
 CONFIG_MAIN_STACK_SIZE=640
 CONFIG_IDLE_STACK_SIZE=200