skip checking dtbs if distro does not support the platform

mkimage.sh

@@ -435,8 +435,18 @@ set -u;
 # if the outer systems happens to be supported by flash-kernel, then these
 # symlinks were written and we remove them to avoid contaminating the chroot
 rm -f /boot/dtb \"/boot/dtb-\$kvers\"
+bookworm_support() {
+    case \$1 in
+        reform-system-imx8mq) return 0;;
+        reform-system-ls1028a) return 0;;
+        *) return 1;;
+    esac;
+};
 for CONF in /usr/share/reform-tools/machines/*.conf; do
     . \"\$CONF\";
+    if [ \"$DIST\" = \"bookworm\" ] && ! bookworm_support \"\$SYSIMAGE\"; then
+           continue;
+    fi;
     echo \"\$DTBPATH\" >&2;
     dtb=\$(find \"/usr/lib/linux-image-\$kvers\" -wholename \"*/\$DTBPATH\" 2>/dev/null | head -n 1);
     echo \"\$dtb\" >&2;