We want to move the definition of use_libpci from gpu/config to ANGLE.
To avoid breaking compilation we should do it in three steps:
 - Make ANGLE not redefine use_libpci
 - Remove definition of use_libpci from Chrome
 - Make ANGLE define use_libpci unconditionnaly

This commit is the first step.

BUG=angleproject:1874

Change-Id: I08d0996ca536c51e1617f656171d696f05605725
Reviewed-on: https://chromium-review.googlesource.com/450037Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>