ARM: dts: rockchip: Add label devicetree property to gpio-leds subnodes

The leds-gpio driver recently switched to the device property API. The device_node
name is no longer retrieved if the "label" devicetree property is not found.
In this case the driver tries to create /sys/class/leds entries with (null) name,
which is wrong and generates a backtrace as several gpio_leds have the same name.
Also renaming subnode "yellow" to "blue" according to the last schematics updates.

Signed-off-by: Romain Perier <romain.perier@gmail.com>