Vulkan: Refactor config generation out of platform specific code. Permuatations of configs are now generated in platform-independent code and a DisplayVk callback is used to determine native support. BUG=angleproject:2692 Change-Id: Iad450c1a3275239d6bcbc350e8dd8e37470fa8e0 Reviewed-on: https://chromium-review.googlesource.com/1117563 Reviewed-by: Luc Ferron <lucferron@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>