dt-bindings: leds: tca6507: convert to YAML

This converts the tca6507 LED binding to yaml.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Cc: NeilBrown <neilb@suse.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: H. Nikolaus Schaller <hns@goldelico.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Adam Ford <aford173@gmail.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Pavel Machek <pavel@ucw.cz>