soc: qcom: glink: Add support to unregister transport

Add support to signal the link down event and unregister the transport.
All channels associated with a transport are cleaned up during link down
notification and the transport is cleaned up during unregister transport
notification.

Change-Id: Ieec61d9d41fe26bc115ca16662d4424aead7ba75
Signed-off-by: Atish Kumar Patra <apatra@codeaurora.org>
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>
Signed-off-by: Zaheerulla Meer <zmeer@codeaurora.org>