feat(mediatek): add more flexibility of mtk_pm.c

To use power manager function more easier, we add some drivers to let
the implementation easier.

Change-Id: Ibc6e1680c4534592ed37de49da39b6667f468ea1
diff --git a/plat/mediatek/lib/pm/rules.mk b/plat/mediatek/lib/pm/rules.mk
index 77d0408..29265c4 100644
--- a/plat/mediatek/lib/pm/rules.mk
+++ b/plat/mediatek/lib/pm/rules.mk
@@ -12,3 +12,6 @@
 LOCAL_SRCS-y := ${LOCAL_DIR}/mtk_pm.c
 
 $(eval $(call MAKE_MODULE,$(MODULE),$(LOCAL_SRCS-y),$(MTK_BL)))
+
+SUB_RULES-$(CONFIG_MTK_PM_SUPPORT) := $(LOCAL_DIR)/armv${CONFIG_MTK_PM_ARCH}
+$(eval $(call INCLUDE_MAKEFILE,$(SUB_RULES-y)))