EmbeddedGpio only supports one gpio controller in one platform. Now
create PLATFORM_GPIO_CONTROLLER to support multiple gpio controllers
in one platform.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>