soc: qcom: qrtr: APIs for ethernet transport

Provide APIs to be used by the ethernet transport/adaption layer to
interface with qrtr-ethernet driver. Ethernet transport/adaption layer
will use these APIs to:
  1. Let qrtr-ethernet know when the ethernet link is up/down so that
     endpoint registration/deregistration is done as needed.
  2. Provide a function pointer for qrtr-ethernet module to transmit
     data to the ethernet adaption layer.

Change-Id: Ifd1a07aef2fc5cd906128d2bed68574a2ab4c29b
Signed-off-by: Jay Jayanna <jayanna@codeaurora.org>