For a given system we only want one kernel to be built. This change makes
the main kernel recipe provide all of the provides of the various enabled
multilibs hence allowing it to fulfil all the appropriate dependencies.
To make this work a global multilib class file needed to be created.
This patch also enables this multi provider functionality for "allarch"
packages.
[YOCTO #1361]
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
