imx8mq: Generate a single bootable flash.bin again

All i.MX8MQ boards have been converted to binman, which makes it
necessary to flash both flash.bin and u-boot.itb to get a bootable
system. Prior to the conversion, only flash.bin was needed.

Such new requirement breaks existing distro mechanisms to generate the
final binary because the extra u-boot.itb is now required.

Generate a final flash.bin that can be used again as a single bootable
binary to keep the original behavior.

After this change the SPL binary is called spl.bin, which is a more
descriptive name for its purpose, and can still be used standalone (for
example, for secure boot purposes).

Also update imx8mq_evk.rst to remove the u-boot.itb copy step.

This is a cherry-pick of 028abfd9b1 ("imx8mm-evk: Generate a single
bootable flash.bin again") adjusted to apply to i.MX8MQ.

Signed-off-by: Patrick Wildt <patrick@blueri.se>
Reviewed-by: Fabio Estevam <festevam@denx.de>

arch/arm/dts/imx8mq-u-boot.dtsi

@@ -50,7 +50,9 @@
 		};
 	};
 
-	flash {
+	spl {
+		filename = "spl.bin";
+
 		mkimage {
 			args = "-n spl/u-boot-spl.cfgout -T imx8mimage -e 0x7e1000";
 
@@ -119,4 +121,19 @@
 			};
 		};
 	};
+
+	imx-boot {
+		filename = "flash.bin";
+		pad-byte = <0x00>;
+
+		spl: blob-ext@1 {
+			offset = <0x0>;
+			filename = "spl.bin";
+		};
+
+		uboot: blob-ext@2 {
+			offset = <0x57c00>;
+			filename = "u-boot.itb";
+		};
+	};
 };

arch/arm/mach-imx/imx8m/imximage.cfg

@@ -8,4 +8,4 @@
 FIT
 BOOT_FROM	sd
 SIGNED_HDMI	signed_hdmi.bin
-LOADER		mkimage.flash.mkimage	0x7e1000
+LOADER		u-boot-spl-ddr.bin	0x7e1000

doc/board/nxp/imx8mq_evk.rst

@@ -50,7 +50,6 @@ Burn the flash.bin to MicroSD card offset 33KB:
 .. code-block:: bash
 
    $sudo dd if=flash.bin of=/dev/sd[x] bs=1024 seek=33 conv=notrunc
-   $sudo dd if=u-boot.itb of=/dev/sd[x] bs=1024 seek=384 conv=notrunc
 
 Boot
 ----