qapi: Flatten object-add

qapi: Flatten object-add

Mapping object-add to the command line as is doesn't result in nice
syntax because of the nesting introduced with 'props'. This becomes
nicer and more consistent with device_add and netdev_add when we accept
properties for the object on the top level instead.

'props' is still accepted after this patch, but marked as deprecated.

Signed-off-by: Kevin Wolf <[email protected]>
Message-Id: <20200224143008[email protected]>
Acked-by: Stefan Hajnoczi <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>