image_types_zchunk: creates zchunk files for delta

Delta update requires artifacts in Zchunk format. The class adds two new
IMAGE_FSTYPES:

- zck: this is the artifact in zchunk format and should be made
  available for downloading.
- zck.zckheader : this is just the header extracted from the zck file.
  This file should be added to the SWU for delta update.

Signed-off-by: Stefano Babic <sbabic@denx.de>

classes-recipe/image_types_zchunk.bbclass

@@ -0,0 +1,7 @@
+CONVERSIONTYPES += "zck zckheader"
+
+CONVERSION_CMD:zck = "zck --output ${IMAGE_NAME}.${type}.zck -u --chunk-hash-type sha256 ${IMAGE_NAME}.${type}"
+CONVERSION_CMD:zckheader = "dd if=${IMAGE_NAME}.${type} of=${IMAGE_NAME}.${type}.zckheader count=1 bs=`zck_read_header -v ${IMAGE_NAME}.${type} | grep 'Header size' | cut -d ':' -f 2 | tr -d '[:space:]'`"
+
+CONVERSION_DEPENDS_zck = "zchunk-native"
+CONVERSION_DEPENDS_zckheader = "zchunk-native"