octeontx2-af: Add mailbox for CPT stats

Adds a new mailbox to get CPT stats, includes performance
counters, CPT engines status and RXC status.

Signed-off-by: Narayana Prasad Raju Atherya <pathreya@marvell.com>
Signed-off-by: Srujana Challa <schalla@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>