net: stmmac: multiple queues dt configuration

This patch adds the multiple queues configuration in the Device Tree.
It was also created a set of structures to keep the RX and TX queues
configurations to be used in the driver.

Signed-off-by: Joao Pinto <jpinto@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>