When drivers signal that an action is completed, they might be still in the
middle of a SSM and so its callback might not be called properly as part of
the completion.
This could make impossible to chain operations like open->enroll/list with
some drivers (hey, synaptics, I'm looking at you!) when the next operation
is called from the GAsyncReadyCallback of the previous call.
To avoid this to happen, ensure that when a driver completes an operation,
we handle the notification to the caller in a next idle iteration, not to
end up in a possible broken state.
Abstract this by using a function that handles the task return for each
used task type to avoid duplicating similar functions doing all the same
thing
We are actually using the cancel idle source in case the device supports
cancellation, so only connect to the cancellable in such case, and use an
utility function to do it and disconnect and reset the state everywhere.
