imx: imx8mn-evk: convert to OF_UPSTREAM

Convert i.MX8MN-EVK and i.MX8MN-DDR4-EVK to OF_UPSTREAM

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/imx8m/Kconfig b/arch/arm/mach-imx/imx8m/Kconfig
index dd139c1..cb8afce 100644
--- a/arch/arm/mach-imx/imx8m/Kconfig
+++ b/arch/arm/mach-imx/imx8m/Kconfig
@@ -151,6 +151,7 @@
 	select IMX8M_LPDDR4
 	select FSL_CAAM
 	select SPL_CRYPTO if SPL
+	imply OF_UPSTREAM
 
 config TARGET_IMX8MN_DDR4_EVK
 	bool "imx8mn DDR4 EVK board"
@@ -159,6 +160,7 @@
 	select IMX8M_DDR4
 	select FSL_CAAM
 	select SPL_CRYPTO if SPL
+	imply OF_UPSTREAM
 
 config TARGET_IMX8MN_VENICE
 	bool "Support Gateworks Venice iMX8M Nano module"