linux-meta: is uninstallable in trusty-proposed

Britney is reporting that linux-meta in trusty-proposed is not installable:

  linux-hwe-virtual-trusty/arm64 unsatisfiable Depends: linux-headers-virtual-lts-utopic
  linux-image-hwe-virtual-trusty/arm64 unsatisfiable Depends: linux-image-virtual-lts-utopic
  linux-hwe-virtual-trusty/armhf unsatisfiable Depends: linux-headers-virtual-lts-utopic
  linux-image-hwe-virtual-trusty/armhf unsatisfiable Depends: linux-image-virtual-lts-utopic
  linux-hwe-generic-trusty/powerpc unsatisfiable Depends: linux-headers-generic-lts-utopic
  linux-hwe-virtual-trusty/powerpc unsatisfiable Depends: linux-headers-virtual-lts-utopic
  linux-image-hwe-generic-trusty/powerpc unsatisfiable Depends: linux-image-generic-lts-utopic
  linux-image-hwe-virtual-trusty/powerpc unsatisfiable Depends: linux-image-virtual-lts-utopic

This is what is sitting in trusty-proposed produced by linux-lts-utopic:

  $ rmadison -a source -s trusty-proposed linux-lts-utopic
   linux-lts-utopic | 3.16.0-48.64~14.04.1 | trusty-proposed | source
  $ rmadison -s trusty-proposed linux-image-3.16.0-48-generic
   linux-image-3.16.0-48-generic | 3.16.0-48.64~14.04.1 | trusty-proposed | amd64, arm64, armhf, i386, ppc64el
  $ rmadison -s trusty-proposed linux-image-extra-3.16.0-48-generic
   linux-image-extra-3.16.0-48-generic | 3.16.0-48.64~14.04.1 | trusty-proposed | amd64, i386, ppc64el
  $

It seems we are assuming output for powerpc which is simply not built and split packages for arm64 and armhf which are not produced.