Hide libpci pkg-config request behind use_libpci==1 This allows platforms that don't have libpci to configure the code without error. BUG=560948 Change-Id: I155f35108d9be193afed5304b443a6afdf33b077 Reviewed-on: https://chromium-review.googlesource.com/314300 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Stephen Mcgruer <smcgruer@google.com> Tested-by: Jamie Madill <jmadill@chromium.org>