rtc: gemini: Augment DT bindings for Faraday

The Gemini RTC is actually a standard IP block from Faraday
Technology called FTRTC010. Rename the bindings, add the
generic compatible string and add definitions for the two
available clocks.

Cc: devicetree@vger.kernel.org
Cc: Po-Yu Chuang <ratbert@faraday-tech.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>