conf: Move the privateData from virDomainChrDef to virDomainChrSourceDef

conf: Move the privateData from virDomainChrDef to virDomainChrSourceDef

Commit id '5f2a132786' should have placed the data in the host source
def structure since that's also used by smartcard, redirdev, and rng in
order to provide a backend tcp channel.  The data in the private structure
will be necessary in order to provide the secret properly.

This also renames the previous names from "Chardev" to "ChrSource" for
the private data structures and API's