Move GrVkInterface out of public API.

Bug: skia:
Change-Id: I8b73982e4c9372af1c35bfc5e665c2c146d7d9f5
Reviewed-on: https://skia-review.googlesource.com/141121
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
14 files changed