octeontx2-af: cn10k: MAC internal loopback support

MAC on CN10K silicon support loopback for selftest or debug purposes.
This patch does necessary configuration to loopback packets upon receiving
request from LMAC mapped RVU PF's netdev via mailbox.

Also MAC (CGX) on OcteonTx2 silicon variants and MAC (RPM) on
OcteonTx3 CN10K are different and loopback needs to be configured
differently. Upper layer interface between RVU AF and PF netdev is
kept same. Based on silicon variant appropriate fn() pointer is
called to config the MAC.

Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: Geetha sowjanya <gakula@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>