* Microsemi - vsc8531 Giga bit ethernet phy

Required properties:
- compatible	: Should contain phy id as "ethernet-phy-idAAAA.BBBB"
		  The PHY device uses the binding described in
		  Documentation/devicetree/bindings/net/phy.txt

Optional properties:
- vsc8531,vddmac	: The vddmac in mV.
- vsc8531,edge-slowdown	: % the edge should be slowed down relative to
			  the fastest possible edge time. Native sign
			  need not enter.
			  Edge rate sets the drive strength of the MAC
			  interface output signals.  Changing the drive
			  strength will affect the edge rate of the output
			  signal.  The goal of this setting is to help
			  reduce electrical emission (EMI) by being able
			  to reprogram drive strength and in effect slow
			  down the edge rate if desired.  Table 1 shows the
			  impact to the edge rate per VDDMAC supply for each
			  drive strength setting.
			  Ref: Table:1 - Edge rate change below.

Note: see dt-bindings/net/mscc-phy-vsc8531.h for applicable values

Table: 1 - Edge rate change
----------------------------------------------------------------|
| 		Edge Rate Change (VDDMAC)			|
|								|
| 3300 mV	2500 mV		1800 mV		1500 mV		|
|---------------------------------------------------------------|
| Default	Deafult		Default		Default		|
| (Fastest)			(recommended)	(recommended)	|
|---------------------------------------------------------------|
| -2%		-3%		-5%		-6%		|
|---------------------------------------------------------------|
| -4%		-6%		-9%		-14%		|
|---------------------------------------------------------------|
| -7%		-10%		-16%		-21%		|
|(recommended)	(recommended)					|
|---------------------------------------------------------------|
| -10%		-14%		-23%		-29%		|
|---------------------------------------------------------------|
| -17%		-23%		-35%		-42%		|
|---------------------------------------------------------------|
| -29%		-37%		-52%		-58%		|
|---------------------------------------------------------------|
| -53%		-63%		-76%		-77%		|
| (slowest)							|
|---------------------------------------------------------------|

Example:

        vsc8531_0: ethernet-phy@0 {
                compatible = "ethernet-phy-id0007.0570";
                vsc8531,vddmac		= <3300>;
                vsc8531,edge-slowdown	= <21>;
        };