octeontx2-vf: Virtual function driver support

On OcteonTx2 silicon there two two types VFs, VFs that share the
physical link with their parent SR-IOV PF and the VFs which work
in pairs using internal HW loopback channels (LBK). Except for the
underlying Rx/Tx channel mapping from netdev functionality perspective
they are almost identical. This patch adds netdev driver support
for these VFs.

Unlike it's parent PF a VF cannot directly communicate with admin
function (AF) and it has to go through PF for the same. The mailbox
communication with AF works like 'VF <=> PF <=> AF'.

Also functionality wise VF and PF are identical, hence to avoid code
duplication PF driver's APIs are resued here for HW initialization,
packet handling etc etc ie almost everything. For VF driver to compile
as module exported few of the existing PF driver APIs.

Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Geetha sowjanya <gakula@marvell.com>
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>