allow dependency between agl feature

allow dependency between agl feature

  * you can add included.inc file for each feature
  * if features is include into an other feature,
    they are print during the --help command

  #source meta-agl/scripts/aglsetup.sh -h
   ...
  Available features:
   [meta-agl]
       agl-all-features :( agl-demo  agl-appfw-smack  agl-devel  agl-netboot  agl-sota )
       agl-archiver
       agl-devel
       agl-isafw
       agl-netboot
   [meta-agl-devel]
       agl-renesas-kernel
   [meta-agl-extra]
       agl-appfw-smack
       agl-demo :( agl-appfw-smack agl-devel)

Change-Id: I4a72abd48f70a9262203acba84fac24d9dd4dce0
Signed-off-by: Ronan <ronan.lemartret@iot.bzh>