rpmsg: glink: Send READ_NOTIFY command in FIFO full case

[ Upstream commit b16a37e1846c9573a847a56fa2f31ba833dae45a ]

The current design sleeps unconditionally in TX FIFO full case and
wakeup only after sleep timer expires which adds random delays in
clients TX path.

Avoid sleep and use READ_NOTIFY command so that writer can be woken up
when remote notifies about read completion by sending IRQ.

Signed-off-by: Deepak Kumar Singh <deesin@codeaurora.org>
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/1596086296-28529-7-git-send-email-deesin@codeaurora.org


Stable-dep-of: 06c59d97f63c ("rpmsg: glink: use only lower 16-bits of param2 for CMD_OPEN name length")
Signed-off-by: Sasha Levin <sashal@kernel.org>