* Microsemi - vsc8531 Giga bit ethernet phy

Optional properties:
- vsc8531,vddmac	: The vddmac in mV. Allowed values is listed
			  in the first row of Table 1 (below).
			  This property is only used in combination
			  with the 'edge-slowdown' property.
			  Default value is 3300.
- vsc8531,edge-slowdown	: % the edge should be slowed down relative to
			  the fastest possible edge time.
			  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.
			  To adjust the edge-slowdown, the 'vddmac'
			  must be specified. Table 1 lists the
			  supported edge-slowdown values for a given
			  'vddmac'.
			  Default value is 0%.
			  Ref: Table:1 - Edge rate change (below).
- vsc8531,led-[N]-mode	: LED mode. Specify how the LED[N] should behave.
			  N depends on the number of LEDs supported by a
			  PHY.
			  Allowed values are defined in
			  "include/dt-bindings/net/mscc-phy-vsc8531.h".
			  Default values are VSC8531_LINK_1000_ACTIVITY (1),
			  VSC8531_LINK_100_ACTIVITY (2),
			  VSC8531_LINK_ACTIVITY (0) and
			  VSC8531_DUPLEX_COLLISION (8).
- load-save-gpios	: GPIO used for the load/save operation of the PTP
			  hardware clock (PHC).


Table: 1 - Edge rate change
----------------------------------------------------------------|
| 		Edge Rate Change (VDDMAC)			|
|								|
| 3300 mV	2500 mV		1800 mV		1500 mV		|
|---------------------------------------------------------------|
| 0%		0%		0%		0%		|
| (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	= <7>;
                vsc8531,led-0-mode	= <VSC8531_LINK_1000_ACTIVITY>;
                vsc8531,led-1-mode	= <VSC8531_LINK_100_ACTIVITY>;
		load-save-gpios		= <&gpio 10 GPIO_ACTIVE_HIGH>;
        };