octeontx2-af: optimize cpt pf identification

[ Upstream commit 9adb04ff ]

Optimize CPT PF identification in mbox handling for faster
mbox response by doing it at AF driver probe instead of
every mbox message.

Signed-off-by: Srujana Challa <schalla@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: a88e0f93 ("octeontx2: Detect the mbox up or down message via register")
Signed-off-by: Sasha Levin <sashal@kernel.org>