kernel.bbclass: add deploy link to KERNEL_IMAGETYPE

It's common to provide a non-machine-suffixed link in DEPLOY_DIR_IMAGE, so
let's be consistent and do so here as well.

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>