dt-bindings: net: qrtr: Add Ethernet Device transport bindings

The QRTR Ethernet driver acts as a transport driver for a device that is
configured as an ethernet endpoint. Document the bindings for this qrtr
transport.

This is dependent on the QTI Ethernet adaption module to enable
communication using ethernet.

Change-Id: Ib96ee45d89a8aef2211233a18d04fb643bb00e14
Signed-off-by: Jay Jayanna <jayanna@codeaurora.org>