board/beaglebone: skip bonegreen.dtb if not built

The beaglebone_qt5_defconfig uses an older kernel version which does not
provide a device tree for the beagle bone green.
post-image.sh now selects genimage_linux41.cfg if am335x-bonegreen.dtb is
not build and genimage.cfg otherwise.

Signed-off-by: Lothar Felten <lothar.felten@gmail.com>
[Thomas: minor tweaks.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/beaglebone/genimage_linux41.cfg

@@ -0,0 +1,32 @@
+image boot.vfat {
+	vfat {
+		files = {
+			"MLO",
+			"u-boot.img",
+			"zImage",
+			"uEnv.txt",
+			"am335x-evm.dtb",
+			"am335x-evmsk.dtb",
+			"am335x-bone.dtb",
+			"am335x-boneblack.dtb",
+		}
+	}
+	size = 16M
+}
+
+image sdcard.img {
+	hdimage {
+	}
+
+	partition u-boot {
+		partition-type = 0xC
+		bootable = "true"
+                image = "boot.vfat"
+	}
+
+	partition rootfs {
+		partition-type = 0x83
+		image = "rootfs.ext4"
+		size = 512M
+	}
+}

board/beaglebone/post-image.sh

@@ -8,7 +8,15 @@ BOARD_DIR="$(dirname $0)"
 # copy the uEnv.txt to the output/images directory
 cp board/beaglebone/uEnv.txt $BINARIES_DIR/uEnv.txt
 
-GENIMAGE_CFG="${BOARD_DIR}/genimage.cfg"
+# the 4.1 kernel does not provide a dtb for beaglebone green, so we
+# use a different genimage config if am335x-bonegreen.dtb is not
+# built:
+if [ -e ${BINARIES_DIR}/am335x-bonegreen.dtb ] ; then
+	GENIMAGE_CFG="${BOARD_DIR}/genimage.cfg"
+else
+	GENIMAGE_CFG="${BOARD_DIR}/genimage_linux41.cfg"
+fi
+
 GENIMAGE_TMP="${BUILD_DIR}/genimage.tmp"
 
 rm -rf "${GENIMAGE_TMP}"