net: arc_emac: add phy reset is optional for device tree

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@rock-chips.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc; Alexander Kochetkov <al.kochet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/arc_emac.txt

@@ -7,6 +7,13 @@ Required properties:
 - max-speed: see ethernet.txt file in the same directory.
 - phy: see ethernet.txt file in the same directory.
 
+Optional properties:
+- phy-reset-gpios : Should specify the gpio for phy reset
+- phy-reset-duration : Reset duration in milliseconds.  Should present
+  only if property "phy-reset-gpios" is available.  Missing the property
+  will have the duration be 1 millisecond.  Numbers greater than 1000 are
+  invalid and 1 millisecond will be used instead.
+
 Clock handling:
 The clock frequency is needed to calculate and set polling period of EMAC.
 It must be provided by one of: