Update rules for util/genvif to allow usb_pd_policy.c to be present
in just baseboard, or just board, or both.
BUG=b:78638238,b:79704826
BRANCH=none
TEST=make -j buildall
Change-Id: I4e2970a65c131d0681d2159fe2ea18b2639048c9
Signed-off-by: Edward Hill <ecgh@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1067751
Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-by: Jett Rink <jettrink@chromium.org>