octeontx2-af: enable tx shaping feature for 96xx C0

Starting from 96xx C0 onwards all silicons support traffic shaping.
This patch enables that feature along with other changes
- When PIR/CIR shaping config is modified, toggle SW_XOFF
  for config to take effect
- Before SMQ flush, clear SW_XOFF at all parent schedulers
- Support to read current transmit scheduler configuration via mbox

Signed-off-by: Nithin Dabilpuram <ndabilpuram@marvell.com>
Signed-off-by: Geetha sowjanya <gakula@marvell.com>
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>