feat(mt8188): initialize GIC

Initialize GIC for mt8188.

TEST=build pass
BUG=b:236331724

Change-Id: I5acf77d654f1bbce32e9fbb3f3567600b7db10ed
diff --git a/plat/mediatek/drivers/gic600/mt_gic_v3.h b/plat/mediatek/drivers/gic600/mt_gic_v3.h
index 98835f0..31513ef 100644
--- a/plat/mediatek/drivers/gic600/mt_gic_v3.h
+++ b/plat/mediatek/drivers/gic600/mt_gic_v3.h
@@ -23,5 +23,6 @@
 void gic_sgi_restore_all(void);
 uint32_t mt_irq_get_pending(uint32_t irq);
 void mt_irq_set_pending(uint32_t irq);
+int mt_gic_one_init(void);
 
 #endif /* MT_GIC_V3_H */