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 <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Alistair Francis <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

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

···
   vdd-supply:
     description: Regulator for voltage.
 
+  vddio-supply:
+    description: Optional Regulator for I/O voltage.
+
   reset-gpios:
     maxItems: 1