unicore: Drop pointless include

I can't see why this file includes <linux/gpio.h>, it is not
using any of the interfaces. Lots of things are named "gpio"
in the file but it is an irqchip driver and has nothing to
do with the GPIO interfaces.

Cc: Guan Xuetao <gxt@pku.edu.cn>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20190626093418.6263-1-linus.walleij@linaro.org