rpmsg: glink: Handle remote rx done command

Once the remote side sends a rx done ack, check for the intent reuse
information from it and suitably discard or reuse the remote passed
intent buffers.

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>