bus: mhi: core: Fix MHI runtime_pm behavior

bus: mhi: core: Fix MHI runtime_pm behavior

This change ensures that PM reference is always get during packet
queueing and released either after queuing completion (RX) or once
the buffer has been consumed (TX). This guarantees proper update for
underlying MHI controller runtime status (e.g. last_busy timestamp)
and prevents suspend to be triggered while TX packets are flying,
or before we completed update of the RX ring.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/1617700315-12492-1-git-send-email-loic.poulain@linaro.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>