This patch adds the following property for arc_emac.
1) phy-reset-gpios:
The phy-reset-gpio is an optional property for arc emac device tree boot.
Change the binding document to match the driver code.
2) phy-reset-duration:
Different boards may require different phy reset duration. Add property
phy-reset-duration for device tree probe, so that the boards that need
a longer reset duration can specify it in their device tree.
Anyway, we can add the above property for arc emac.
Signed-off-by: Caesar Wang <wxt@xxxxxxxxxxxxxx>