gpio: eic-sprd: Make the irqchip immutable

Remove the irq_chip from pmic_eic structure,
use the various calls by defining the statically
irq_chip structure.

Signed-off-by: Cixi Geng <cixi.geng1@unisoc.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>