imx: imx8mn_ddr4_evk: Use CONFIG_TARGET_IMX8MN_DDR4_EVK for DDR4 EVK board

use CONFIG_TARGET_IMX8MN_DDR4_EVK for DDR4 EVK board, we will use
CONFIG_TARGET_IMX8MN_EVK for LPDDR4 EVK board.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/configs/imx8mn_ddr4_evk_defconfig b/configs/imx8mn_ddr4_evk_defconfig
index 41889c4..f7ea658 100644
--- a/configs/imx8mn_ddr4_evk_defconfig
+++ b/configs/imx8mn_ddr4_evk_defconfig
@@ -12,7 +12,7 @@
 CONFIG_SYS_I2C_MXC_I2C3=y
 CONFIG_DM_GPIO=y
 CONFIG_SPL_TEXT_BASE=0x912000
-CONFIG_TARGET_IMX8MN_EVK=y
+CONFIG_TARGET_IMX8MN_DDR4_EVK=y
 CONFIG_SPL_MMC_SUPPORT=y
 CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL_DRIVERS_MISC_SUPPORT=y