imx8mp: binman: rename spl and u-boot nodes

The hab signing script doc/imx/habv4/csf_examples/mx8m/csf.sh does

  fdtget -t x u-boot.dtb /binman/imx-boot/uboot offset

to figure out the offset of u-boot.itb inside flash.bin. That works
fine for imx8mm, imx8mn, imx8mq, but fails for imx8mp because in that
case 'uboot' is merely a label and not actually the node name.

Homogenize these cases and make imx8mp the same as the other imx8m*
variants. The binman type is explicitly given and no longer derived
from the node name, and the csf.sh script will work for all four SOCs.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Fabio Estevam <festevam@denx.de>

arch/arm/dts/imx8mp-u-boot.dtsi

@@ -200,14 +200,16 @@
 		filename = "flash.bin";
 		pad-byte = <0x00>;
 
-		spl: blob-ext@1 {
+		spl {
 			filename = "spl.bin";
 			offset = <0x0>;
+			type = "blob-ext";
 		};
 
-		uboot: blob-ext@2 {
+		binman_uboot: uboot {
 			filename = "u-boot.itb";
 			offset = <0x58000>;
+			type = "blob-ext";
 		};
 	};
 };