dt-bindings: net: dsa: realtek: reset-gpios is not required

The 'reset-gpios' should not be mandatory. although they might be
required for some devices if the switch reset was left asserted by a
previous driver, such as the bootloader.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Cc: devicetree@vger.kernel.org
Acked-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>