net: mvpp2: adapt rxq distribution to PPv2.2

In PPv2.1, we have a maximum of 8 RXQs per port, with a default of 4
RXQs per port, and we were assigning RXQs 0->3 to the first port, 4->7
to the second port, 8->11 to the third port, etc.

In PPv2.2, we have a maximum of 32 RXQs per port, and we must allocate
RXQs from the range of 32 RXQs available for each port. So port 0 must
use RXQs in the range 0->31, port 1 in the range 32->63, etc.

This commit adapts the mvpp2 to this difference between PPv2.1 and
PPv2.2:

 - The constant definition MVPP2_MAX_RXQ is replaced by a new field
   'max_port_rxqs' in 'struct mvpp2', which stores the maximum number of
   RXQs per port. This field is initialized during ->probe() depending
   on the IP version.

 - MVPP2_RXQ_TOTAL_NUM is removed, and instead we calculate the total
   number of RXQs by multiplying the number of ports by the maximum of
   RXQs per port. This was anyway used in only one place.

 - In mvpp2_port_probe(), the calculation of port->first_rxq is adjusted
   to cope with the different allocation strategy between PPv2.1 and
   PPv2.2. Due to this change, the 'next_first_rxq' argument of this
   function is no longer needed and is removed.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>