D3D11: Futher optimize input layout cache. Using the new vertex format type enum, we can shrink the size of the input layout tables and reduce draw call overhead further. BUG=angleproject:959 Change-Id: Iea595fa64edbbd91f669138dfdeb9d2543b83929 Reviewed-on: https://chromium-review.googlesource.com/277291 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Kenneth Russell <kbr@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>