Hide console access behind an interface

Hide console access behind an interface

* Allows a different implementation of the console protocol for
  non-default consoles.

Signed-off-by: Owen Smith <owen.smith@citrix.com>
* Re-worked create/destroy and renamed some items.
* Left IsDefault as a flag on the Pdo.
* Fail to create the PDO in the non-default case.
* ASSERT the Pdo is default before attempting to use the ABI, since it
  is only valid in this case.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>