board/stm32f469-disco: move kernel and DTB to rootfs partition

The patch, following the suggestion expressed in the review [1] for the
stm32f746-disco board support, moves the Linux kernel and the related
device tree to the ext4 rootfs partition. By doing so, the vfat partition,
improperly called u-boot, no longer makes sense and can therefore be
removed. From now on, U-Boot will load the kernel and the device tree
from the ext4 rootfs partition.

While we're at it, also fix shellcheck warnings in the post-build script.

[1] https://patchwork.ozlabs.org/project/buildroot/patch/20240822183742.3550055-3-dario.binacchi@amarulasolutions.com/

Suggested-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>

board/stmicroelectronics/stm32f469-disco/extlinux.conf

@@ -1,4 +1,4 @@
 label stm32f469-disco-buildroot
-  kernel /zImage
-  devicetree /stm32f469-disco.dtb
-  append console=ttySTM0,115200 root=/dev/mmcblk0p2 rw rootfstype=ext2 rootwait earlyprintk consoleblank=0 ignore_loglevel
+  kernel /boot/zImage
+  devicetree /boot/stm32f469-disco.dtb
+  append console=ttySTM0,115200 root=/dev/mmcblk0p1 rw rootfstype=ext2 rootwait earlyprintk consoleblank=0 ignore_loglevel

board/stmicroelectronics/stm32f469-disco/genimage.cfg

@@ -1,24 +1,7 @@
-image boot.vfat {
-	vfat {
-		files = {
-			"zImage",
-			"stm32f469-disco.dtb",
-			"extlinux"
-		}
-	}
-
-	size = 16M
-}
-
 image sdcard.img {
 	hdimage {
 	}
 
-	partition u-boot {
-		partition-type = 0xC
-		image = "boot.vfat"
-	}
-
 	partition rootfs {
 		partition-type = 0x83
 		image = "rootfs.ext2"

board/stmicroelectronics/stm32f469-disco/post-build.sh

@@ -1,4 +1,4 @@
 #!/bin/sh
-BOARD_DIR="$(dirname $0)"
+BOARD_DIR="$(dirname "$0")"
 
-install -m 0644 -D $BOARD_DIR/extlinux.conf $BINARIES_DIR/extlinux/extlinux.conf
+install -m 0644 -D "${BOARD_DIR}"/extlinux.conf "${TARGET_DIR}"/boot/extlinux/extlinux.conf