Vulkan: Move vulkan config target to $angle_root:vulkan_config This will allow us to avoid loading the build file for //third_party/vulkan-validation-layers on Fuchsia, since we don't want to build the validation layers on that platform. BUG=angleproject:2475 TEST=angle_end2end_tests on Fuchsia (with full series) Change-Id: Ifeb67125f5fcebf2b30ae18b760667ba7c56e4d5 Reviewed-on: https://chromium-review.googlesource.com/c/1456479 Commit-Queue: Michael Spang <spang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>