dt-bindings: trivial-devices: add isil,isl69260

dt-bindings: trivial-devices: add isil,isl69260

Document the "isl,isl69260" compatible, which is already used in the
DTS files but was not previously documented in the bindings.
The ISL69260 is a digital dual output multiphase controller
that supports Intel VR13, VR13.HC, and VR14 specifications.

Signed-off-by: Peter Yin <peteryin.openbmc@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20240809070056.3588694-1-peteryin.openbmc@gmail.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>