Vulkan: Make flushAfterVertexConversion workaround Nexus5X-specific Workaround added in 611bbaabb28cf4231ad0a138cd7bc21fe559ea02 is likely Nexus5X-specific. This commit detects the phone and enables the workaround only on that. Bug: angleproject:2958, angleproject:3009 Change-Id: I9ab230d4aa690fd92e3d2d84ad98c159128c1093 Reviewed-on: https://chromium-review.googlesource.com/c/1372445 Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>