octeontx2-af: avoid RXC register access for CN10KB

This patch modifies the driver to prevent access to RXC hardware
registers on the CN10KB, as RXC is not available on this chip.

Signed-off-by: Srujana Challa <schalla@marvell.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>