dt-bindings: hwmon: Add UCD90320 gpio description

Add optional gpio device tree bindings to the UCD90320.
The binding's description is already mentioning the number of GPIOs but
without actual gpio controller description.

Signed-off-by: Jonathan Stroud <jonathan.stroud@amd.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/662a050f3f8160fe7c80d4f19e45eb4fac0f2f0a.1740384385.git.michal.simek@amd.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>