D3D11: Optimize sample caps checks. We don't need to check NPOT sample counts. This should save us some time on eglInitialize. BUG=angleproject:1014 Change-Id: Id3b0a440689746d5de9a7fbc3641ff9452b18601 Reviewed-on: https://chromium-review.googlesource.com/274430 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>