layerscape: problems with image builder

[Martin Schiller]

When trying to build an image for the Layerscape "NXP LS1046A-RDB SD
Card Boot" target using Image Builder, you get the following error
messages:

------------------------------------------------------------------------
...
Package list missing or not up-to-date, generating it.

Building package index...
Downloading file:packages/Packages
Updated list of available packages in <XXX>
Downloading file:packages/Packages.sig
Signature check passed.
Collected errors:
  * opkg_install_cmd: Cannot install package fmc.
  * opkg_install_cmd: Cannot install package fmc-eth-config.
  * opkg_install_cmd: Cannot install package layerscape-fman.
  * opkg_install_cmd: Cannot install package tfa-ls1046a-rdb-sdboot.
make[3]: *** [Makefile:167: package_install] Error 255
make[2]: *** [Makefile:132: _call_manifest] Error 2
make[1]: *** [Makefile:251: manifest] Error 2
...
------------------------------------------------------------------------

The following is noticeable:
1. All these packages are listed in the "DEVICES_PACKAGES" of this
    target.
2. the packages "fmc" and "fmc-eth-config" do not exist at all.
3. the packages "layerscape-fman" and "tfa-ls1046a-rdb-sdboot" do not
    have a "package/install" routine and therefore do not create an ipk
    file. Only binary blobs are installed via "Build/InstallDev", which
    are then used during image assembly.

Since "fmc" and "fmc-eth-config" do not exist, we should remove these
entries from the "DEVICE_PACKAGES".

For the other two it is a bit more difficult. For this, a mechanism
similar to PKG_BUILD_DEPENDS on image level would be useful or
necessary.

Any suggestions?

- Martin