Add floating point EGL configs for the D3D11 backend.

BUG=angleproject:1707

Change-Id: Ic84cd3a0d41e78cc39d0275d83e7695f55673ddf
Reviewed-on: https://chromium-review.googlesource.com/428294
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>