arm64: dts: imx8m: Always name the generated fitImage u-boot.itb

Maintain backward compatibility with pre-binman u-boot file naming,
the U-Boot fitImage used to be named u-boot.itb before, restore the
file name after binman conversion.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/dts/imx8mn-u-boot.dtsi b/arch/arm/dts/imx8mn-u-boot.dtsi
index 732191f..6875c6d 100644
--- a/arch/arm/dts/imx8mn-u-boot.dtsi
+++ b/arch/arm/dts/imx8mn-u-boot.dtsi
@@ -193,6 +193,7 @@
 
 			binman_imx_fit: fit {
 				description = "Configuration to load ATF before U-Boot";
+				filename = "u-boot.itb";
 #ifndef CONFIG_IMX_HAB
 				fit,external-offset = <CONFIG_FIT_EXTERNAL_OFFSET>;
 #endif