amd-xgbe: Prepare for priority-based FIFO allocation

Currently, the Rx and Tx fifos are evenly allocated between the hardware
queues of the device.  As more queues are instantiated, the fifo memory
needs to be able to be allocated based on queue priority. This allows for
higher priority queues to have more fifo memory than lower priority
queues. Prepare for this by modifying the current fifo calculation to
assign the fifo queue allocation in an array that is then used to program
the hardware.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>