boards: convert SiFive HiFive Unleashed to Zephyr HWMv2

This commit converts the SiFive HiFive Unleashed board (`hifive_unleashed`
target) to the Zephyr Hardware Model v2.

Signed-off-by: Filip Kokosinski <fkokosinski@antmicro.com>

boards/sifive/hifive_unleashed/Kconfig.defconfig

@@ -1,15 +1,13 @@
 # Copyright (c) 2021 Katsuhiro Suzuki
+# Copyright (c) 2024 Antmicro <www.antmicro.com>
 # SPDX-License-Identifier: Apache-2.0
 
 if BOARD_HIFIVE_UNLEASHED
 
-config BOARD
-	default "hifive_unleashed"
-
 config SYS_CLOCK_TICKS_PER_SEC
 	default 1000
 
 config SYS_CLOCK_HW_CYCLES_PER_SEC
 	default 1000000
 
-endif
+endif # BOARD_HIFIVE_UNLEASHED

boards/sifive/hifive_unleashed/Kconfig.hifive_unleashed

@@ -2,5 +2,4 @@
 # SPDX-License-Identifier: Apache-2.0
 
 config BOARD_HIFIVE_UNLEASHED
-	bool "HiFive Unleashed target"
-	depends on SOC_SIFIVE_FREEDOM_U540
+	select SOC_SIFIVE_FREEDOM_FU540

boards/sifive/hifive_unleashed/board.yml

@@ -0,0 +1,5 @@
+board:
+  name: hifive_unleashed
+  vendor: sifive
+  socs:
+    - name: fu540

boards/sifive/hifive_unleashed/hifive_unleashed_defconfig

@@ -1,6 +1,5 @@
-CONFIG_SOC_SERIES_SIFIVE_FREEDOM_U500=y
-CONFIG_SOC_SIFIVE_FREEDOM_U540=y
-CONFIG_BOARD_HIFIVE_UNLEASHED=y
+# SPDX-License-Identifier: Apache-2.0
+
 CONFIG_CONSOLE=y
 CONFIG_GPIO=y
 CONFIG_SERIAL=y