[BUG]-DmRmcControllerBase could possibly fail to register endpoints

[TrevorPayne]

Describe the bug The constructor of DmRmcHelper utilizes the instance of the chassis returned by DeviceManager. If the chassis has not yet been instantiated, the returned device will be null and the endpoint will remain unregistered.

Expected behavior The individual device instantiation should move into one of the activation phases, after it's certain that the DeviceManager has already been populated by all devices.