dt-bindings: net: convert net/cortina,gemini-ethernet to yaml

Converts net/cortina,gemini-ethernet.txt to yaml
This permits to detect some missing properties like interrupts

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220201144940.2488782-1-clabbe@baylibre.com