boards: Convert stm32f746g_disco to HWM v2

Port the board to HWMv2.

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

boards/boards_legacy/arm/stm32f746g_disco/Kconfig.board

@@ -1,8 +0,0 @@
-# STM32F746G Discovery board configuration
-
-# Copyright (c) 2018 Yurii Hamann
-# SPDX-License-Identifier: Apache-2.0
-
-config BOARD_STM32F746G_DISCO
-	bool "STM32F746G Discovery Development Board"
-	depends on SOC_STM32F746XX

boards/st/stm32f746g_disco/Kconfig.defconfig

@@ -5,9 +5,6 @@
 
 if BOARD_STM32F746G_DISCO
 
-config BOARD
-	default "stm32f746g_disco"
-
 if NETWORKING
 
 config NET_L2_ETHERNET

boards/st/stm32f746g_disco/Kconfig.stm32f746g_disco

@@ -0,0 +1,5 @@
+# Copyright (c) 2018 Yurii Hamann
+# SPDX-License-Identifier: Apache-2.0
+
+config BOARD_STM32F746G_DISCO
+	select SOC_STM32F746XX

boards/st/stm32f746g_disco/board.yml

@@ -0,0 +1,5 @@
+board:
+  name: stm32f746g_disco
+  vendor: st
+  socs:
+    - name: stm32f746xx

boards/st/stm32f746g_disco/stm32f746g_disco_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