meson.bbclass: Prevent meson from downloading wrapped projects

Meson has support for downloading subprojects using something called
wraps. This interferes with bitbake's expectations of all downloads
being done by the fetch task. To avoid this, tell meson to not
download any wraps.

Suggested-by: Mattias Jernberg <mattias.jernberg@axis.com>
Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>