octeontx2-af: Skip PFs if not enabled

Firmware enables PFs and allocate mbox resources for each of the PFs.
Currently PF driver configures mbox resources without checking whether
PF is enabled or not. This results in crash. This patch fixes this issue
by skipping disabled PF's mbox initialization.

Fixes: 9bdc47a6 ("octeontx2-af: Mbox communication support btw AF and it's VFs")
Signed-off-by: Ratheesh Kannoth <rkannoth@marvell.com>
Signed-off-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Sai Krishna <saikrishnag@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>