octeontx2-af: Enable sriov on AF to create VFs

Enable all AF VFs during probe. Since AF's VFs work in pairs
(eg: Pkts sent on VF0 are received by VF1 and viceversa),
enable only even number of VFs out of totalVFs, which should
again be less than number of loopback (LBK) channels.

Also enable VF's mailbox interrupts.

Signed-off-by: Tomasz Duszynski <tduszynski@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>