Some users of ANGLE might want to use the D3D11 backend on older
Windows 7 platforms that only support DXGI 1.1. DXGI 1.1 doesn't
recognize the FL 11.1 enum passed to D3D11CreateDevice, so special
fall-back code is needed to fall back to FL 11.0 or lower in this
case.

BUG=angleproject:2173

Change-Id: Id77401d0e2a16786ed44d117ca746908e8d0892c
Reviewed-on: https://chromium-review.googlesource.com/716356Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>