[Graphite] Rename DawnUtilsPriv to DawnGraphiteUtilsPriv.

This matches how we handle the naming in other backends and opens the
way to add a shared DawnUtilsPriv file.

Change-Id: Idbef906affa423d2d6fdc93edda749ad8f177ca5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/654540
Commit-Queue: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Auto-Submit: Greg Daniel <egdaniel@google.com>
7 files changed