The libpsl subproject wasn't building successfully and CI didn't
notice because:
1. The plugin wasn't explicitly enabled
2. Even when the plugin is explicitly enabled, the dep is not required
at build time when not building a static plugin
So fix all of these issues.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4890>
libpsl is a dependency if libsoup that has an upstream Meson build
system (in master only).
libsoup also needs libxml2 but we already have a wrap file for it.
The only remaining dependency that must come from the system is sqlite3.
