board/raspberrypi/post-image.sh: generate genimage config from template if not present

The rpi genimage configurations are all identical, except for the boot
partition files, which include:

- Device tree files (*.dtb)
- rpi-firmware files (rpi-firmware/*)
- Kernel image (Image/zImage)

All of these are quite simple to figure out programmatically based on the
content of BINARIES_DIR, so extend post-image.sh to fall back to generating
a genimage configuration based on genimage.cfg.in if a board specific one
does not exist.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/raspberrypi/genimage.cfg.in

@@ -0,0 +1,25 @@
+image boot.vfat {
+	vfat {
+		files = {
+#BOOT_FILES#
+		}
+	}
+
+	size = 32M
+}
+
+image sdcard.img {
+	hdimage {
+	}
+
+	partition boot {
+		partition-type = 0xC
+		bootable = "true"
+		image = "boot.vfat"
+	}
+
+	partition rootfs {
+		partition-type = 0x83
+		image = "rootfs.ext4"
+	}
+}

board/raspberrypi/post-image.sh

@@ -7,6 +7,23 @@ BOARD_NAME="$(basename ${BOARD_DIR})"
 GENIMAGE_CFG="${BOARD_DIR}/genimage-${BOARD_NAME}.cfg"
 GENIMAGE_TMP="${BUILD_DIR}/genimage.tmp"
 
+# generate genimage from template if a board specific variant doesn't exists
+if [ ! -e "${GENIMAGE_CFG}" ]; then
+	GENIMAGE_CFG="${BINARIES_DIR}/genimage.cfg"
+	FILES=()
+
+	for i in "${BINARIES_DIR}"/*.dtb "${BINARIES_DIR}"/rpi-firmware/*; do
+		FILES+=( "${i#${BINARIES_DIR}/}" )
+	done
+
+	KERNEL=$(sed -n 's/^kernel=//p' "${BINARIES_DIR}/rpi-firmware/config.txt")
+	FILES+=( "${KERNEL}" )
+
+	BOOT_FILES=$(printf '\\t\\t\\t"%s",\\n' "${FILES[@]}")
+	sed "s|#BOOT_FILES#|${BOOT_FILES}|" "${BOARD_DIR}/genimage.cfg.in" \
+		> "${GENIMAGE_CFG}"
+fi
+
 # Pass an empty rootpath. genimage makes a full copy of the given rootpath to
 # ${GENIMAGE_TMP}/root so passing TARGET_DIR would be a waste of time and disk
 # space. We don't rely on genimage to build the rootfs image, just to insert a