octeontx2-af: Add Marvell OcteonTX2 RVU AF driver

This patch adds basic template for Marvell OcteonTX2's
resource virtualization unit (RVU) admin function (AF)
driver. Just the driver registration and probe.

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