feat(mt8188): add pinctrl support

Add pinctrl support for MT8188.

TEST=build pass
BUG=b:236331724

Signed-off-by: Jianguo Zhang <jianguo.zhang@mediatek.corp-partner.google.com>
Change-Id: Id4ac8f67009621fff8f15f3ab2d8f200343c8356
diff --git a/plat/mediatek/drivers/gpio/mtgpio_common.h b/plat/mediatek/drivers/gpio/mtgpio_common.h
index 68d96e5..d6b858c 100644
--- a/plat/mediatek/drivers/gpio/mtgpio_common.h
+++ b/plat/mediatek/drivers/gpio/mtgpio_common.h
@@ -104,6 +104,6 @@
 	uint16_t offset;
 };
 
-void mt_gpio_init(void);
+int mt_gpio_init(void);
 uintptr_t mt_gpio_find_reg_addr(uint32_t pin);
 #endif /* MT_GPIO_COMMON_H */