regulator: rt4831: Adds DT binding document for Richtek RT4831 DSV regulator

Adds DT binding document for Richtek RT4831 DSV regulator.
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Link: https://lore.kernel.org/r/1608217244-314-3-git-send-email-u0084500@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/richtek,rt4831-regulator.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/regulator/richtek,rt4831-regulator.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Richtek RT4831 Display Bias Voltage Regulator
+
+maintainers:
+  - ChiYuan Huang <cy_huang@richtek.com>
+
+description: |
+  RT4831 is a multifunctional device that can provide power to the LCD display
+  and LCD backlight.
+
+  For Display Bias Voltage DSVP and DSVN, the output range is about 4V to 6.5V.
+  It is sufficient to meet the current LCD power requirement.
+
+  DSVLCM is a boost regulator in IC internal as DSVP and DSVN input power.
+  Its voltage should be configured above 0.15V to 0.2V gap larger than the
+  voltage needed for DSVP and DSVN. Too much voltage gap could improve the
+  voltage drop from the heavy loading scenario. But it also make the power
+  efficiency worse. It's a trade-off.
+
+  Datasheet is available at
+  https://www.richtek.com/assets/product_file/RT4831A/DS4831A-05.pdf
+
+patternProperties:
+  "^DSV(LCM|P|N)$":
+    type: object
+    $ref: regulator.yaml#
+    description:
+      Properties for single Display Bias Voltage regulator.
+
+additionalProperties: false