gpio: gemini: rename to match Faraday IP

The Gemini driver is actually a driver for the Faraday Technology
FTGPIO010 IP block. We rename the driver and the Kconfig symbol and
put in a a new compatible string for the Moxa ART SoC that is also
using this IP block.

Tested-by: Jonas Jensen <jonas.jensen@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>