gpio: eic-sprd: Optimize the calculation method of eic number

The num_eics is a default value, but some SoCs support more than 8.
In order to adapt to all projects, the total number of eics is
automatically calculated through dts.

Signed-off-by: Wenhua Lin <Wenhua.Lin@unisoc.com>
Acked-by: Chunyan Zhang <zhang.lyra@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>