mhi: cntrl: qcom: disable runtime PM support in a graceful manner

MHI relies on runtime PM framework auto-suspend feature. Initial
approach did not stop the auto-suspend timer or disable runtime
PM at device power down. It also re-initialized internal
variables at power up which resulted in a use after free scenario
as an old timer entry was freed again at a time of core collapse.
Disable runtime PM support gracefully at device power down to
avoid such scenarios.

CRs-Fixed: 2352747
Change-Id: I72f370fc77b04c12fdf2a5cf2a46a94fffa99082
Acked-by: Bhaumik Vasav Bhatt <bbhatt@qti.qualcomm.com>
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>