qapi: Restrict balloon-related commands to machine code

qapi: Restrict balloon-related commands to machine code

Only qemu-system-FOO and qemu-storage-daemon provide QMP
monitors, therefore such declarations and definitions are
irrelevant for user-mode emulation.

Restricting the balloon-related commands to machine.json pulls less
QAPI-generated code into user-mode.

Reviewed-by: David Hildenbrand <[email protected]>
Acked-by: Markus Armbruster <[email protected]>
Acked-by: Paolo Bonzini <[email protected]>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Message-Id: <20200913195348.1064154[email protected]>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <[email protected]>