accel/habanalabs: optimize timestamp registration handler

Currently we use dynamic allocation inside the irq handler
in order to allocate free node to be used for the free jobs.

This operation is expensive, especially when we deal with large
burst of events records that get released at the same time.

The alternative is to have pre allocated pool of free nodes
and just fetch nodes from this pool at irq handling time instead
of allocating them.

In case the pool becomes full, then the driver will fallback to
dynamic allocations.

As part of the optimization also update the unregister flow
upon re-using a timestamp record, by making the operation much
simpler and quicker. We already have the record in the registration
flow and now we just seek to re-use with different interrupt.
Therefore, no need to look for buffer according to the user handle.

Signed-off-by: farah kassabri <fkassabri@habana.ai>
Reviewed-by: Tomer Tayar <ttayar@habana.ai>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>