mhi: core: improve bandwidth switch events processing

We may unnecessarily wake up the device when there is no pending
bandwidth switch request. Avoid that by only asserting device wake if
one is pending. We can also have the underlying MHI bus go to suspend
while a device requested bandwidth switch is yet to be processed.
Prevent host suspends by capturing both bus and device votes and
increment pending packets to reject suspends while the processing is
ongoing.

Change-Id: I4eddb6bf9eaa973be5c0b0ac516269e54599b9f2
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>