Use primaryGPUIndex over activeGPUIndex when determining the system GPU. Mac OPENGL/AMD dEQP test suppressions were being ignored because in SystemInfo the activeGPUIndex was used when the primaryGPUIndex should have been used. Bug: angleproject:3373 Change-Id: I2664049b956bf8903c6d7094ec27646766e7ce16 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1565056 Commit-Queue: Jonah Ryan-Davis <jonahr@google.com> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>