boards: Convert nucleo_f746zg to HWM v2

Port the board to HWMv2.

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

boards/boards_legacy/arm/nucleo_f746zg/Kconfig.board

@@ -1,8 +0,0 @@
-# STM32F746ZG Nucleo board configuration
-
-# Copyright (c) 2018 AJ Palmer
-# SPDX-License-Identifier: Apache-2.0
-
-config BOARD_NUCLEO_F746ZG
-	bool "Nucleo F746ZG Development Board"
-	depends on SOC_STM32F746XX

boards/st/nucleo_f746zg/Kconfig.defconfig

@@ -5,9 +5,6 @@
 
 if BOARD_NUCLEO_F746ZG
 
-config BOARD
-	default "nucleo_f746zg"
-
 if NETWORKING
 
 config NET_L2_ETHERNET

boards/st/nucleo_f746zg/Kconfig.nucleo_f746zg

@@ -0,0 +1,5 @@
+# Copyright (c) 2018 AJ Palmer
+# SPDX-License-Identifier: Apache-2.0
+
+config BOARD_NUCLEO_F746ZG
+	select SOC_STM32F746XX

boards/st/nucleo_f746zg/board.yml

@@ -0,0 +1,5 @@
+board:
+  name: nucleo_f746zg
+  vendor: st
+  socs:
+    - name: stm32f746xx

boards/st/nucleo_f746zg/nucleo_f746zg_defconfig

@@ -1,8 +1,5 @@
 # SPDX-License-Identifier: Apache-2.0
 
-CONFIG_SOC_SERIES_STM32F7X=y
-CONFIG_SOC_STM32F746XX=y
-
 # Enable MPU
 CONFIG_ARM_MPU=y