usb: pd: Allow receiving VDM messages during suspend

Add an API to allow a VDM client (e.g. DisplayPort) to indicate
that the system is entering suspend but that an incoming VDM
message is expected. If a VDM is then received, it will bypass
kick_sm() which would otherwise abort the suspend and instead
be handed to the client VDM handler directly.

The flag can be reset either explicitly, if a soft/hard reset
occur, or if a VDM TX is requested, as those situations would
require the state machine to run in the worker thread normally.

Change-Id: I8af7e13abad766f9e4245149da9457f1c62a25d5
Signed-off-by: Jack Pham <jackp@codeaurora.org>