Replace our implementation of a lockless ring buffer with the standard
linux kernel kfifo.

We shouldn't maintain our own version of a standard data structure.
Signed-off-by: NAndres Rodriguez <andres.rodriguez@amd.com>
Signed-off-by: NFelix Kuehling <Felix.Kuehling@amd.com>
Acked-by: NOded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: NOded Gabbay <oded.gabbay@gmail.com>