octeontx2-af: replace cpt slot with lf id on reg write

Replace slot id with global CPT lf id on reg read/write as
CPTPF/VF driver would send slot number instead of global
lf id in the reg offset. And also update the mailbox response
with the global lf's register offset.

Fixes: ae454086

 ("octeontx2-af: add mailbox interface for CPT")
Signed-off-by: Nithin Dabilpuram <ndabilpuram@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>