core/pkg-infra: really build all dependencies of foo with foo-depends

core/pkg-infra: really build all dependencies of foo with foo-depends

Currently, foo-depends only builds build dependencies. This means that
download and extract dependencies are not built.

First, but a minor point, this is inconsistent with foo-show-depends,
which does display all dependencies:

    $ make host-gzip-show-depends
    host-skeleton host-tar
    $ make host-gzip-depends
        # Only host-skeleton is built and installed

Second, and more important, it makes it more difficult to preapre a
debug build, like so:

    $ make foo-depends
    $ tar cf output.tar output
    $ make foo
        # bummer, broken
        # edit foo.mk to try and fix it
    $ rm -rf output; tar xf output.tar
        # rince and repeat

Change foo-depends so that it really builds all the dependencies for
foo, bringing it on-par with foo-show-depends.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>