boards: arm: efm32hg_slstk3400a: Convert to v2

Converts the board to hwmv2

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

boards/silabs/efm32hg_slstk3400a/Kconfig.defconfig

@@ -5,9 +5,6 @@
 
 if BOARD_EFM32HG_SLSTK3400A
 
-config BOARD
-	default "efm32hg_slstk3400a"
-
 config CMU_HFXO_FREQ
 	default 24000000
 

boards/silabs/efm32hg_slstk3400a/Kconfig.efm32hg_slstk3400a

@@ -4,6 +4,4 @@
 # SPDX-License-Identifier: Apache-2.0
 
 config BOARD_EFM32HG_SLSTK3400A
-	bool "SiLabs EFM32HG-SLSTK3400A (Happy Gecko)"
-	depends on SOC_SERIES_EFM32HG
 	select SOC_PART_NUMBER_EFM32HG322F64

boards/silabs/efm32hg_slstk3400a/board.yml

@@ -0,0 +1,5 @@
+board:
+  name: efm32hg_slstk3400a
+  vendor: silabs
+  socs:
+  - name: efm32hg322f64

boards/silabs/efm32hg_slstk3400a/efm32hg_slstk3400a_defconfig

@@ -1,7 +1,5 @@
 # SPDX-License-Identifier: Apache-2.0
 
-CONFIG_SOC_SERIES_EFM32HG=y
-CONFIG_BOARD_EFM32HG_SLSTK3400A=y
 CONFIG_CONSOLE=y
 CONFIG_UART_CONSOLE=y
 CONFIG_SERIAL=y