Palmas RTC controller bindings

Required properties:
- compatible:
  - "ti,palmas-rtc" for palma series of the RTC controller
- interrupt-parent: Parent interrupt device, must be handle of palmas node.
- interrupts: Interrupt number of RTC submodule on device.

Optional properties:

- ti,backup-battery-chargeable: The Palmas series device like TPS65913 or
	TPS80036 supports the backup battery for powering the RTC when main
	battery is removed or in very low power state. The backup battery
	can be chargeable or non-chargeable. This flag will tells whether
	battery is chargeable or not. If charging battery then driver can
	enable the charging.
- ti,backup-battery-charge-high-current: Enable high current charging in
	backup battery. Device supports the < 100uA and > 100uA charging.
	The high current will be > 100uA. Absence of this property will
	charge battery to lower current i.e. < 100uA.

Example:
	palmas: tps65913@58 {
		...
		palmas_rtc: rtc {
			compatible = "ti,palmas-rtc";
			interrupt-parent = <&palmas>;
			interrupts = <8 0>;
			ti,backup-battery-chargeable;
			ti,backup-battery-charge-high-current;
		};
		...
	};