rpmsg: glink: Integrate glink_ssr in qcom_glink

In all but the very special case of a system with _only_ glink_rpm,
GLINK is dependent on glink_ssr, so move it to rpmsg and combine it with
qcom_glink_native in the new qcom_glink kernel module.

Acked-by: Chris Lew <clew@codeaurora.org>
Acked-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
Link: https://lore.kernel.org/r/20200423003736.2027371-4-bjorn.andersson@linaro.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>