ucsi: ucsi_glink: Notify upon change in connector status

Add APIs to allow clients to register for (and unregister from)
receiving notifications whenever a response is received for a
GET_CONNECTOR_STATUS request. Currently the notifications contain only a
single field indicating whether or not a Debug Accessory or an Audio
Adapter Accessory is attached (parsed from the received response).

Change-Id: If1ef46f5f9e4b4fa93f32bfd06fd50c7e16f7874
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>