QPNP PMIC BUCK current monitoring

QPNP PMIC BUCK provides two current limiting interrupts INT1(icritical) and
INT2(iwarn), which gets trigger whenever buck load current crosses the
programmed threshold (INT1/INT2 interrupt triggers whenever load current
crosses INT1_CURRENT/INT2_CURRENT threshold respectively).
These interrupts are used for MSM current throttling.

[PMIC BUCK current monitor Device Declarations]

Required properties:
- compatible : should be "qcom,qpnp-buck-current-monitor".
- reg : offset and length of the PMIC Aribter register map.
- interrupts : Specifies critical and warning interrupt.
- interrupt-names : Should contain "iwarn", "icritical".

Optional properties:
- qcom,icrit-init-threshold-pc :   Initial critical current threshold in
				percentage of maximum rated current (3 Amps).
				If this	value is not specified default is 90%
				of rated current.
- qcom,iwarn-init-threshold-pc :   Initial warning current threshold in
				percentage of maximum rated current (3 Amps).
				If this value is not specified default is 70%
				of rated current.
- qcom,icrit-polling-delay-msec : Delay for polling RT status register for
				  ICRIT interrupt.
- qcom,iwarn-polling-delay-msec : Delay for polling RT status register for
				  IWARN interrupt.
- qcom,enable-current-monitor : Enable current monitor. If this property is
				not specified buck will not generate current
				limiting interrupts unless explictly enabled
				from user-space.

Example:
	qpnp-buck-current-monitor@1800 {
			compatible = "qcom,qpnp-buck-current-monitor";
			reg = <0x1800 0x100>;
			interrupts = <1 0x18 0>, <1 0x18 1>;
			interrupt-names = "iwarning", "icritical";
			qcom,icrit-init-threshold-pc = <90>;
			qcom,iwarn-init-threshold-pc = <70>;
			qcom,icrit-polling-delay-msec = <1000>;
			qcom,iwarn-polling-delay-msec = <2000>;
			qcom,enable-current-monitor;
	};
