package/pkg-generic: add <pkg>-show-recursive-(r)depends targets

package/pkg-generic: add <pkg>-show-recursive-(r)depends targets

This commit adds the support for <pkg>-show-recursive-depends and
<pkg>-show-recursive-rdepends which respectively show the list of all
dependencies or reverse dependencies for a given package. The existing
show-depends and show-rdepends only show the first-level dependencies,
while show-recursive-depends and show-recursive-rdepends show
recursively the dependencies.

It is worth mentioning that while show-recursive-depends really shows
all dependencies, show-recursive-rdepends is a bit limited because the
reverse dependencies of host packages are not properly accounted
for. But that's a limitation that already exists in show-rdepends, and
that cannot easily be solved.

Signed-off-by: George Redivo <george.redivo@datacom.ind.br>
[Thomas:
 - split from the patch that was also changing graph-depends
 - rename show-rrdepends to show-recursive-rdepends
 - add show-recursive-depends
 - don't create GRAPHS_DIR.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>