dt-bindings: leds: convert ktd2692 bindings to yaml

This patch converts the leds-ktd2692.txt bindings to modern yaml
style device-tree bindings.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Markuss Broks <markuss.broks@gmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>