Voltage/Current regulator

Binding:
The regulator devices don't use the "compatible" property. The binding is done
by the prefix of regulator node's name, or, if this fails, by the prefix of the
regulator's "regulator-name" property. Usually the pmic I/O driver will provide
the array of 'struct pmic_child_info' with the prefixes and compatible drivers.
The bind is done by calling function: pmic_bind_childs().
Example drivers:
pmic: drivers/power/pmic/max77686.c
regulator: drivers/power/regulator/max77686.c

For the node name e.g.: "prefix[:alpha:]num { ... }":
- the driver prefix should be: "prefix" - case sensitive
- the node name's "num" is set as "dev->driver_data" on bind

Example the prefix "ldo" will pass for: "ldo1", "ldo@1", "ldoreg@1, ...

Binding by means of the node's name is preferred. However if the node names
would produce ambiguous prefixes (like "regulator@1" and "regualtor@11") and you
can't or do not want to change them then binding against the "regulator-name"
property is possible. The syntax for the prefix of the "regulator-name" property
is the same as the one for the regulator's node name.
Use case: a regulator named "regulator@1" to be bound to a driver named
"LDO_DRV" and a regulator named "regualator@11" to be bound to an other driver
named "BOOST_DRV". Using prefix "regualtor@1" for driver matching would load
the same driver for both regulators, hence the prefix is ambiguous.

Optional properties:
- regulator-name: a string, required by the regulator uclass, used for driver
                  binding if binding by node's name prefix fails
- regulator-min-microvolt: a minimum allowed Voltage value
- regulator-max-microvolt: a maximum allowed Voltage value
- regulator-min-microamp: a minimum allowed Current value
- regulator-max-microamp: a maximum allowed Current value
- regulator-always-on: regulator should never be disabled
- regulator-boot-on: enabled by bootloader/firmware
- regulator-ramp-delay: ramp delay for regulator (in uV/us)

Note
The "regulator-name" constraint is used for setting the device's uclass
platform data '.name' field. And the regulator device name is set from
it's node name. If "regulator-name" is not provided in dts, node name
is chosen for setting the device's uclass platform data '.name' field.

Other kernel-style properties, are currently not used.

Note:
For the regulator autoset from constraints, the framework expects that:
- regulator-min-microvolt is equal to regulator-max-microvolt
- regulator-min-microamp is equal to regulator-max-microamp
- regulator-always-on or regulator-boot-on is set

Example:
ldo0 {
	/* Optional */
	regulator-name = "VDDQ_EMMC_1.8V";
	regulator-min-microvolt = <1800000>;
	regulator-max-microvolt = <1800000>;
	regulator-min-microamp = <100000>;
	regulator-max-microamp = <100000>;
	regulator-always-on;
	regulator-boot-on;
	regulator-ramp-delay = <12000>;
};
