AM335x Power Management bindings

Support for VTT Toggle

In order to enable the support for VTT toggle during Suspend/Resume
sequence needed by some boards (like AM335x EVM-SK & AM437x GP EVM),
below DT properties needs to be added under the M3 Wakeup Node.

Required properties:
- ti,needs-vtt-toggle:	Indicates that the boards requires VTT toggling
			during suspend/resume.
- ti,vtt-gpio-pin:	Specifies the GPIO pin used for VTT toggle.

Important Note:
- Here it is assumed that VTT Toggle will be done using a pin on GPIO-0 Instance

Example:
	wkup_m3: wkup_m3@44d00000 {
		compatible = "ti,am3353-wkup-m3";
		...
		...
		ti,needs-vtt-toggle;
		ti,vtt-gpio-pin = <7>;
	};
