Add ability to do deterministic convolutions for cudnn

[coreylowman]

This would involve filtering the results in the three pick_algorithm methods for only ones that are marked as deterministic.

Since I don't want this to be a breaking change, let's add a 2nd method alongside pick_algorithm that looks like:

pub fn pick_algorithm(&self) -> ... {
    self.pick_algorithm_ex(false)
}

pub fn pick_algorithm_ex(&self, force_deterministic: bool) -> ... {
    // existing pick_algorithm code, but with the filtering based on force_deterministic passed in
     ....
}