With the intention of reusing the glink core protocol commands and code
across both rpm and smem based transports, the only thing different is
way of accessing the shared-memory of the transport (FIFO). So put the
fifo accessor's of the transport's pipe (rx/tx) behind indirections, so
that the rest of the code can be shared.

For this, have a qcom_glink_pipe that can be used in the common code
containing the indirections and wrap it with glink_rpm_pipe that
contains the transport specific members.
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>