arm: dts: imx8m: update binman ddr firmware node name

We are migrating to use binman symbols, the current names are
inconsistent across different boards, so unify them.

Also add `type = "blob-ext";`, since the new names are not valid binman
types.

Tested-by: Tim Harvey <tharvey@gateworks.com> #imx8m[m,n,p]-venice
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
[Alper: Edit commit message]
Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
diff --git a/arch/arm/dts/imx8mn-ddr4-evk-u-boot.dtsi b/arch/arm/dts/imx8mn-ddr4-evk-u-boot.dtsi
index 4d0ecb0..30ef8bc 100644
--- a/arch/arm/dts/imx8mn-ddr4-evk-u-boot.dtsi
+++ b/arch/arm/dts/imx8mn-ddr4-evk-u-boot.dtsi
@@ -155,24 +155,28 @@
 			align-end = <4>;
 		};
 
-		blob_1: blob-ext@1 {
+		ddr-1d-imem-fw {
 			filename = "ddr4_imem_1d_201810.bin";
 			size = <0x8000>;
+			type = "blob-ext";
 		};
 
-		blob_2: blob-ext@2 {
+		ddr-1d-dmem-fw {
 			filename = "ddr4_dmem_1d_201810.bin";
 			size = <0x4000>;
+			type = "blob-ext";
 		};
 
-		blob_3: blob-ext@3 {
+		ddr-2d-imem-fw {
 			filename = "ddr4_imem_2d_201810.bin";
 			size = <0x8000>;
+			type = "blob-ext";
 		};
 
-		blob_4: blob-ext@4 {
+		ddr-2d-dmem-fw {
 			filename = "ddr4_dmem_2d_201810.bin";
 			size = <0x4000>;
+			type = "blob-ext";
 		};
 	};