support/scripts: use show-info to extract dependency graph

Currently, we extract the dependency graph from the aptly named but
ad-hoc show-dependency-graph rule.

We now have a better solution to report package information, with
show-info.

Since show-dependency-graph never went into a release so far, and
show-info does provide the same (and more), switch to using show-info.

Thanks to Adam for suggesting the coding style to have a readable code
that is not ugly but still pleases flake8. Thanks to Arnout for
suggesting the use of dict.get() to further simplify the code.

Note: we do not use the reverse_dependencies field because it only
contains those packages that have a kconfig option, so we'd miss most
host packages.

Reported-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Adam Duskett <aduskett@gmail.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>