feat(plat/mediatek/mt8186): initialize systimer

Add systimer to support timer function.

TEST=build pass
BUG=b:202871018

Change-Id: I505f7d094410d178e4203e3a9294b851a30ba150
diff --git a/plat/mediatek/mt8186/platform.mk b/plat/mediatek/mt8186/platform.mk
index 7e962de..46e2050 100644
--- a/plat/mediatek/mt8186/platform.mk
+++ b/plat/mediatek/mt8186/platform.mk
@@ -8,6 +8,7 @@
 MTK_PLAT_SOC := ${MTK_PLAT}/${PLAT}
 
 PLAT_INCLUDES := -I${MTK_PLAT}/common/                            \
+                 -I${MTK_PLAT}/common/drivers/timer/              \
                  -I${MTK_PLAT_SOC}/drivers/emi_mpu/               \
                  -I${MTK_PLAT_SOC}/include/
 
@@ -28,6 +29,7 @@
                 plat/common/plat_gicv3.c                              \
                 ${MTK_PLAT}/common/mtk_plat_common.c                  \
                 ${MTK_PLAT}/common/params_setup.c                     \
+                ${MTK_PLAT}/common/drivers/timer/mt_timer.c           \
                 ${MTK_PLAT_SOC}/aarch64/platform_common.c             \
                 ${MTK_PLAT_SOC}/aarch64/plat_helpers.S                \
                 ${MTK_PLAT_SOC}/bl31_plat_setup.c                     \