meson: default to gpl=disabled for gst-plugins-bad and -ugly

meson: default to gpl=disabled for gst-plugins-bad and -ugly

This will only affect individual/tarball module builds, as the
options yield to the parent project which was set to gpl=disabled
by default already. We kept it as auto in the original commit
to accommodate the need to update cerbero as well, which had to
be done separately after the initial commit.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1217>