gpio: gemini: augment DT bindings

The DT bindings assumed that this IP block was coming from
Cortina Systems, which turns out not to be true. It is a
standard IP block from Faraday Technology and also used in the
Moxa moxart SoC.

We augment the bindings to cover all existing parts and rename
it after the IP block. This involves deleting the old Moxa
bindings that now are contained in this binding.

Cc: devicetree@vger.kernel.org
Cc: Jonas Jensen <jonas.jensen@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>