feat(mt8188): add reset and poweroff functions

- Add mtk_pm_system_reset_cros() for cros reset.
- Add mtk_pm_system_off_cros() for cros power-off.

TEST=build pass
BUG=b:236331724

Change-Id: I4117f6080e282551b37a936a490ab7b37ac31827
diff --git a/plat/mediatek/mt8188/platform.mk b/plat/mediatek/mt8188/platform.mk
index a50f750..a76dff3 100644
--- a/plat/mediatek/mt8188/platform.mk
+++ b/plat/mediatek/mt8188/platform.mk
@@ -22,6 +22,7 @@
 MODULES-y += $(MTK_PLAT)/common
 MODULES-y += $(MTK_PLAT)/lib/mtk_init
 MODULES-y += $(MTK_PLAT)/lib/pm
+MODULES-y += $(MTK_PLAT)/lib/system_reset
 MODULES-y += $(MTK_PLAT)/drivers/cirq
 MODULES-y += $(MTK_PLAT)/drivers/dp
 MODULES-y += $(MTK_PLAT)/drivers/gic600