riscv: sifive: fu540: Use OTP DM driver for serial environment variable

Use the OTP DM driver to set the serial environment variable.

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/board/sifive/fu540/Kconfig b/board/sifive/fu540/Kconfig
index 75661f3..4330ac4 100644
--- a/board/sifive/fu540/Kconfig
+++ b/board/sifive/fu540/Kconfig
@@ -51,5 +51,7 @@
 	imply SIFIVE_GPIO
 	imply CMD_GPIO
 	imply SMP
+	imply MISC
+	imply SIFIVE_OTP
 
 endif