docs: Deprecate incorrectly typed device_add arguments

docs: Deprecate incorrectly typed device_add arguments

While introducing a non-QemuOpts code path for device creation for JSON
-device, we noticed that QMP device_add doesn't check its input
correctly (accepting arguments that should have been rejected), and that
users may be relying on this behaviour (libvirt did until it was fixed
recently).

Let's use a deprecation period before we fix this bug in QEMU to avoid
nasty surprises for users.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20211111143530.18985-1-kwolf@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20211115145409.176785-12-kwolf@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>