After real world use its clear the "multiconfig:" prefix to multiconfig tasks,
whilst clear, is also clumbersome. Switch to use the short version instead.
mcdepends will continue to work with "multiconfig:" for now as well. The commandline
will only accept mc: going forward.
[YOCTO #11168]
(Bitbake rev: 821daf093b76504067a8b77dfa4b181af6ec92b4)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>