yocto.groovy: Build SWUpdate artifacts for the RaspberryPi 3
yocto.groovy: Build SWUpdate artifacts for the RaspberryPi 3

This introduces CI support for the core-image-pelux-*-update recipes.
Those recipes are currently only available for the Raspberry Pi 3
therefore a check is done to only build when variant_name starts with
rpi.

Signed-off-by: Florent Revest <f3a243d30ac77beaf87c86f4ee386884cad18cf5@gmail.com>

sashko/pelux-manifests,Pelagicore/pelux-manifests