regulator: dt-bindings: Document charger-supply for max8997

Add charger-supply optional property to enable charging control.
Signed-off-by: Timon Baetz <timon.baetz@protonmail.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20210130172747.2022977-2-timon.baetz@protonmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/max8997-regulator.txt

@@ -35,6 +35,7 @@ Optional properties:
 - interrupts: Interrupt specifiers for two interrupt sources.
   - First interrupt specifier is for 'irq1' interrupt.
   - Second interrupt specifier is for 'alert' interrupt.
+- charger-supply: regulator node for charging current.
 - max8997,pmic-buck1-uses-gpio-dvs: 'buck1' can be controlled by gpio dvs.
 - max8997,pmic-buck2-uses-gpio-dvs: 'buck2' can be controlled by gpio dvs.
 - max8997,pmic-buck5-uses-gpio-dvs: 'buck5' can be controlled by gpio dvs.