dt-bindings: input: cyttsp5: document vddio-supply

The Samsung touchscreen controllers are often used with external pull-up
for the interrupt line and the I2C lines, so we might need to enable
a regulator to bring the lines into usable state. Otherwise, this might
cause spurious interrupts and reading from I2C will fail.

Document support for a "vddio-supply" that is enabled by the cyttsp5
driver so that the regulator gets enabled when needed.
Signed-off-by: Lin, Meng-Bo <linmengbo0689@protonmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Alistair Francis <alistair@alistair23.me>
Link: https://lore.kernel.org/r/20221117190507.87535-2-linmengbo0689@protonmail.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/cypress,tt21000.yaml

@@ -34,6 +34,9 @@ properties:
   vdd-supply:
     description: Regulator for voltage.
 
+  vddio-supply:
+    description: Optional Regulator for I/O voltage.
+
   reset-gpios:
     maxItems: 1