riscv: configs: AE350 will use CONFIG_OF_PRIOR_STAGE when boots from ram

When AE350 boots from ram, use CONFIG_OF_PRIOR_STAGE instead
of CONFIG_OF_BOARD.

Signed-off-by: Rick Chen <rick@andestech.com>
Cc: Greentime Hu <greentime@andestech.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
diff --git a/configs/ae350_rv64_defconfig b/configs/ae350_rv64_defconfig
index 287769d..d425252 100644
--- a/configs/ae350_rv64_defconfig
+++ b/configs/ae350_rv64_defconfig
@@ -15,7 +15,7 @@
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_BOOTP_PREFER_SERVERIP=y
 CONFIG_CMD_CACHE=y
-CONFIG_OF_BOARD=y
+CONFIG_OF_PRIOR_STAGE=y
 CONFIG_DEFAULT_DEVICE_TREE="ae350_64"
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_NET_RANDOM_ETHADDR=y