greybus: operation: add helper for creating core operations

Add a new core operation flag and a helper that core can use to create
core operations.

This will be used to implement the ping operations that core sends as
part of connection tear down.

Note that a new trace point is also added.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>