octeontx2-af: add mbox for CPT LF reset

On OcteonTX2 SoC, the admin function (AF) is the only one with all
priviliges to configure HW and alloc resources, PFs and it's VFs
have to request AF via mailbox for all their needs.
This patch adds a new mailbox for CPT VFs to request for CPT LF
reset.

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