Melange should create the subpkgdirs

[justinvreeland]

As I've been working on usr-merge I've noticed many packages that assume the subpkgdir exists, I did too. In some cases this results in packages that were created in a way would have been usr-merged but because the subpkgdir isn't already created un-usrmerges the package. Below is an example of where the removed line intended to move the usr/ directory into the ${{targets.subpkgdir}} but instead the usr directory becomes the top-level subpkgdir.

   - name: ntfs-3g-progs
     pipeline:
       - runs: |
-          mv ${{targets.destdir}}/usr ${{targets.destdir}}/lib ${{targets.subpkgdir}}/
+          mkdir -p ${{targets.subpkgdir}}
+          mv ${{targets.destdir}}/usr ${{targets.subpkgdir}}