octeontx2-af: Add FEC stats for RPM/RPM_USX block

CN10K silicon MAC block RPM and CN10KB silicon MAC block RPM_USX
both support BASER and RSFEC modes.

Also MAC (CGX) on OcteonTx2 silicon variants and MAC (RPM) on
OcteonTx3 CN10K are different and FEC stats need to be read
differently. CN10KB MAC block (RPM_USX) fec csr offsets are same
as CN10K MAC block (RPM) mac_ops points to same fn(). Upper layer
interface between  RVU AF and PF netdev is  kept same. Based on
silicon variant appropriate fn() pointer is called to  read FEC stats

Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>