riscv: sifive: Rename fu540 board to unleashed

In preparation to add SiFive Unmatched board support, let's rename
the existing fu540 board to unleashed.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
diff --git a/drivers/reset/Kconfig b/drivers/reset/Kconfig
index f5b3f88..019565f 100644
--- a/drivers/reset/Kconfig
+++ b/drivers/reset/Kconfig
@@ -166,7 +166,7 @@
 
 config RESET_SIFIVE
 	bool "Reset Driver for SiFive SoC's"
-	depends on DM_RESET && CLK_SIFIVE_FU540_PRCI && TARGET_SIFIVE_FU540
+	depends on DM_RESET && CLK_SIFIVE_FU540_PRCI && TARGET_SIFIVE_UNLEASHED
 	default y
 	help
 	  PRCI module within SiFive SoC's provides mechanism to reset