stmmac: adding new glue driver dwmac-dwc-qos-eth

This patch adds a new glue driver called dwmac-dwc-qos-eth which
was based in the dwc_eth_qos as is. To assure retro-compatibility a slight
tweak was also added to stmmac_platform.

Signed-off-by: Joao Pinto <jpinto@synopsys.com>
Tested-by: Niklas Cassel <niklas.cassel@axis.com>
Reviewed-by: Lars Persson <larper@axis.com>
Acked-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>