Mediatek MT6370 DSV display bias subdev
MT6370 display bias control.

Required properties:
- compatible : Must be "mediatek,mt6370_pmu_dsv";
- interrupt-names : MT6370 dsv enabled interrupts.
	(R:required, O:optional)
	1. dsv_vneg_ocp: vneg's over current flag.
	2. dsv_vpos_ocp: vpos's over current flag.
	3. dsv_bst_ocp: boost voltage of DB's over circuit.
	4. dsv_vneg_scp: vneg's short circuit protection.
	5. dsv_vpos_scp: vpos's short circuit protection.

- db_ext_en : 0 for i2c control, 1 for external pin control.
- db_periodic_fix : 0 disable, 1 -> prevent from voltage drop when db is restart.
- db_single_pin : 0 -> vpos and vneg are controlled by db_enp and db_enm,
		  1 -> single pin control.
- db_freq_pm : 0 -> 20Hz, 1 -> 33Hz, the value is valid only when db_period_mode = 1.
- db_periodic_mode : 0 = always on if db is enabled; 1 = DB period mode.
- db_startup : 0 -> close loop, wait 80%; 1 = open loop, go after soft-start dimming.
- db_vneg_20ms : 0 disable, 1 -> DB_VNEG discharge 20ms when shutdown.
- db_vneg_disc : 0 disable, 1 -> discharge vneg when turn off.
- db_vpos_20ms : 0 disable, 1 -> DB_VPOS discharge 20ms when shutdown.
- db_vpos_disc : 0 disable, 1 -> discharge vpos when turn off.
- db_delay : 0 no constraint, 1 -> 0ms, 2 -> 1ms, 3, 4ms.
- db_vbst : vboost voltage, need greater than dsv_pos & dsv_neg 200mV.
- db_vpos_slew : 0 -> 8.46 V/ms, 1 -> 5.79 V/ms, 2 -> 3.87 V/ms, 3 -> 2.97 V/ms.
- db_vneg_slew : 0 -> -9.24V/ms, 1 -> -5.97V/ms, 2 -> -4.82V/ms, 3 -> -3.07V/ms.

Optional node:

Child node:
- mt6370_dsvn : mt6370_dsv vneg initial setting.
- mt6370_dsvp : mt6370_dsv vpos initial setting.

Example:
mt6370_pmu@34 {
	status = "ok";
	compatible = "mediatek,mt6370_pmu";
	reg = <0x34>;
	interrupt-controller;
	#interrupt-cells = <1>;
	mt6370,intr_gpio_num = <3>; /* direct defined GPIO num */
	mt6370,intr_gpio = <&pio 3 0>; /* genernal GPIO */
	dsv {
		compatible = "mediatek,mt6370_pmu_dsv";
		interrupt-names = "dsv_vneg_ocp", "dsv_vpos_ocp",
				  "dsv_bst_ocp", "dsv_vneg_scp",
				  "dsv_vpos_scp";
		db_ext_en = <0>;  /* 0 = i2c ctrl; 1 = ext pin */
		db_periodic_fix = <0>; /* 1 = prevent from voltage drop when db is restart */
		db_single_pin = <0>; /* 0 => VOS & VNEG are ctrled by DB_ENP & DB_ENN; 1 : single pin ctrl*/
		db_freq_pm = <0>; /*  0 = 20Hz ; 1 = 33Hz; valid if db_period_mode = 1 */
		db_periodic_mode = <0>; /* 0 = always on if DB is enabled; 1 = DB period mode */
		db_startup = <0>; /* 0 = close loop, wait 80%; 1 = open loop, go after soft-start dimming */
		db_vneg_20ms = <1>; /* 1 = DB VNEG discharge 20ms when shutdown; 0 = disable */
		db_vneg_disc = <0>; /*  1 = Discharge VNEG when turn off; 0 = disable */
		db_vpos_20ms = <1>; /* 1 = DB VPOS discharge 20ms when shutdown; 0 = disable */
		db_vpos_disc = <0>; /*  1 = Discharge VPOS when turn off; 0 = disable */
		db_delay = <3>; /* 0 = no constraint; 1 = 0 ms; 2 = 1 ms; 3 = 4 ms */
		db_vbst  = <5700>; /* mV */
		db_vpos_slew = <1>; /* 0 : 8.46 V/ms; 1 : 5.79 V/ms; 2: 3.87 V/ms; 3: 2.97V/ms */
		db_vneg_slew = <1>; /* 0: -9.24V/ms; 1: -5.97V/ms; 2: -4.82V/ms; 3: -3.07V/ms*/
		mt6370_dsvp {
			regulator-name = "dsv_pos"; /* change name by yourself */
			regulator-min-microvolt = <4000000>;
			regulator-max-microvolt = <6000000>; /* max == min then apply_uV = 1 */
			/* regulator-microvolt-offset = < 0>; optional*/
			/* regulator-boot-on = "yes"; optional, exist = enabled */
			/* regulator-always-on = "yes"; optional, exist = enabled */
			/* regulator-ramp-delay = <100>; optional*/
		};
		mt6370_dsvn {
			regulator-name = "dsv_neg"; /* change name by yourself */
			regulator-min-microvolt = <4000000>;
			regulator-max-microvolt = <6000000>; /* max == min then apply_uV = 1 */
			/* regulator-microvolt-offset = < 0>; optional*/
			/* regulator-boot-on = "yes"; optional, exist = enabled */
			/* regulator-always-on = "yes"; optional, exist = enabled */
			/* regulator-ramp-delay = <100>; optional*/
		};
	};
};
