dt-bindings: socfpga-dwmac: add "altr, socfpga-stmmac-a10-s10" binding

Add the "altr,socfpga-stmmac-a10-s10" binding for Arria10/Agilex/Stratix10
implementation of the stmmac ethernet controller.

On the Arria10, Agilex, and Stratix10 SoCs, there are a few differences from
the Cyclone5 and Arria5:
     - The emac PHY setup bits are in separate registers.
     - The PTP reference clock select mask is different.
     - The register to enable the emac signal from FPGA is different.

Because of these differences, the dwmac-socfpga glue logic driver will
use this new binding to set the appropriate bits for PHY, PTP reference
clock, and signal from FPGA.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>