octeontx2-af: NIX Tx scheduler queues alloc/free

Added support for a PF/VF to allocate or free NIX transmit
scheduler queues via mbox. For setting up pkt transmission
priorities between queues, the scheduler queues have to be
contiguous w.r.t their HW indices. So both contiguous and
non-contiguous allocations are supported.

Upon receiving NIX_TXSCH_FREE mbox msg all scheduler queues
allocated to sending PFFUNC (PF/VF) will be freed. Selective
free is not supported.

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