rpmsg: glink: Add support for transport version negotiation

G-link supports a version number and feature flags for each transport.
A combination of the version number and feature flags enable/disable:

 (*) G-Link software updates for each edge
 (*) Individual features for each edge

Endpoints negotiate both the version and the supported flags when
the transport is opened and they cannot be changed after negotiation has
been completed.

Each full implementation of G-Link must support a minimum of the current
version, the previous version, and the base negotiation version called v0.

Acked-by: Arun Kumar Neelakantam <aneela@codeaurora.org>
Signed-off-by: Sricharan R <sricharan@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>