octeontx2-af: Add Marvell OcteonTX2 CGX driver

This patch adds basic template for Marvell OcteonTX2's
CGX ethernet interface driver. Just the probe.
RVU AF driver will use APIs exported by this driver
for various things like PF to physical interface mapping,
loopback mode, interface stats etc. Hence marged both
drivers into a single module.

Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>