qapi: Split control.json off misc.json

misc.json contains definitions that are related to the system emulator,
so it can't be used for other tools like the storage daemon. This patch
moves basic functionality that is shared between all tools (and mostly
related to the monitor itself) into a new control.json, which could be
used in tools as well.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200129102239.31435-3-kwolf@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>