char: virtio_eavb: Add virtio_eavb frontend driver

This driver provides unified interface for applications, and communicate
with backend. So applications run in GVM but use backend eavb stack.

Change-Id: Ief3d033e5477696fa336e7225b58867fbf6aac5e
Signed-off-by: Baowei Liu <baowei@codeaurora.org>