Vulkan: Optimize ContextVk::updateDefaultAttributes. This function was getting called every time because the dirty bit mask included dirty bits for unused program attributes. Fix this by making sure we never have dirty bits set for inactive attributes. Bug: angleproject:2786 Change-Id: Icf72dadd8a853d3a448abb303119b7b71f6c8193 Reviewed-on: https://chromium-review.googlesource.com/1188951 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Frank Henigman <fjhenigman@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>