CI: Azure: Split keymile jobs out

Currently the PowerPC build job in Azure will hit the maximum time limit
for a build and stop. Looking at the job, the easiest path to reducing
it is to move Keymile vendor boards to their own job and exclude them
from the PowerPC one (and while at this, the ls102 job).

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Heiko Schocher <hs@denx.de>