Add DXGI_FORMAT to BackendFormat.

First steps to getting D3D texture format caps set up.

Bug: skia:9935
Change-Id: I905aaedd7d5fcc8b5137fcc8d8189e93260c9359
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/273797
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
2 files changed