octeontx2-af: Disable backpressure between CPT and NIX

NIX can assert backpressure to CPT on the NIX<=>CPT link.
Keep the backpressure disabled for now. NIX block anyways
handles backpressure asserted by MAC due to PFC or flow
control pkts.

Signed-off-by: Bharat Bhushan <bbhushan2@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>