octeontx2-af: NIX Tx scheduler queue config support

This patch adds support for a PF/VF driver to configure
NIX transmit scheduler queues via mbox. Since PF/VF doesn't
know the absolute HW index of the NIXLF attached to it, AF
traps the register config and overwrites with the correct
NIXLF index.

HW supports shaping, colouring and policing of packets with
these multilevel traffic scheduler queues. Instead of
introducing different mbox message formats for different
configurations and making both AF & PF/VF driver implementation
cumbersome, access to the scheduler queue's CSRs is provided
via mbox. AF checks whether the sender PF/VF has the
corresponding queue allocated or not and dumps the config
to HW. With a single mbox msg 20 registers can be configured.

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