nfp: devlink port split support for 1x100G CXP NIC

[ Upstream commit 5948185b97fa1f83d7855e638a72982a1073ebf5 ]

This commit makes it possible to use devlink to split the 100G CXP
Netronome into two 40G interfaces. Currently when you ask for 2
interfaces, the math in src/nfp_devlink.c:nfp_devlink_port_split
calculates that you want 5 lanes per port because for some reason
eth_port.port_lanes=10 (shouldn't this be 12 for CXP?). What we really
want when asking for 2 breakout interfaces is 4 lanes per port. This
commit makes that happen by calculating based on 8 lanes if 10 are
present.

Signed-off-by: Ryan C Goodfellow <rgoodfel@isi.edu>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Greg Weeks <greg.weeks@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>