octeontx2-af: cn10k: DWRR MTU configuration

On OcteonTx2 DWRR quantum is directly configured into each of
the transmit scheduler queues. And PF/VF drivers were free to
config any value upto 2^24.

On CN10K, HW is modified, the quantum configuration at scheduler
queues is in terms of weight. And SW needs to setup a base DWRR MTU
at NIX_AF_DWRR_RPM_MTU / NIX_AF_DWRR_SDP_MTU. HW will do
'DWRR MTU * weight' to get the quantum. For LBK traffic, value
programmed into NIX_AF_DWRR_RPM_MTU register is considered as
DWRR MTU.

This patch programs a default DWRR MTU of 8192 into HW and also
provides a way to change this via devlink params.

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