Fix common include priority for p500

PRODUCT_COPY_FILES: First definition wins if the file name is the same. Most specific first.
DEVICE_PACKAGE_OVERLAYS: Last definition wins. Most specific last.
CONFIG := xxx: Last definition wins. Most specific last.

TESTED ON: configs/wpa_supplicant.conf

Change-Id: I574a419fe07bcfa2cadd834bd16998c29acff94c