[L0v2] fix unbounded memory growth of queue's submitted kernels

[pbalcer]

L0v2 avoids internally tracking each kernel submission through an event for lifetime management. Instead, when a kernel is submitted to the queue, its handle is added to a vector, to be removed at the next queue synchronization point, urQueueFinish(). This is a much more efficient way of handling kernel tracking, since it avoids taking and storing an event. However, if the application never synchronizes the queue, this vector of submitted kernels will grow unbounded.

This patch forcibly synchronizes the queue once the submitted kernels vector reaches a threshold.

[pbalcer]

I've created a PR against 6.2, since this functionality changed a little in the latest version, and will require a different patch.