I am building the Android Open Source Project (AOSP) from source for the Pine 64 board using the community v6 version. One of the things I needed to do was add a pre-compiled .apk file to the /system/priv-app folder. Finding information on how to create an Android.mk file to do that was really difficult. Below is the Android.mk file that I finally came up with.
LOCAL_PATH := $(call my-dir)
# Module name should match apk name to be installed.
LOCAL_MODULE := MyModule
LOCAL_SRC_FILES := $(LOCAL_MODULE).apk
LOCAL_MODULE_CLASS := APPS
LOCAL_MODULE_SUFFIX := $(COMMON_ANDROID_PACKAGE_SUFFIX)
LOCAL_PACKAGE_NAME := MyModule
LOCAL_CERTIFICATE := shared
LOCAL_PRIVILEGED_MODULE := true
# If its a launcher / home App (which mine is) set this
LOCAL_OVERRIDES_PACKAGES := Home