ARM: vf610: use zero based naming for GPIO nodes

On Vybrid, all peripherals are numbered starting with zero,
including the GPIO and PORT module. However, the labels of the
corresponding device tree nodes start with one, which is confusing.
Fix that by renaming the labels of the gpio nodes in the device
tree.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>