riscv: sifive: fu540: Setup ethaddr env variable using OTP

This patch extends SiFive FU540 board support to setup ethaddr
env variable based on board serialnum read from OTP.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/sifive_fu540_defconfig b/configs/sifive_fu540_defconfig
index f784123..f192037 100644
--- a/configs/sifive_fu540_defconfig
+++ b/configs/sifive_fu540_defconfig
@@ -7,4 +7,5 @@
 CONFIG_FIT=y
 CONFIG_DISPLAY_CPUINFO=y
 CONFIG_DISPLAY_BOARDINFO=y
+CONFIG_MISC_INIT_R=y
 CONFIG_OF_PRIOR_STAGE=y