Add GrVkInterface constructor with sepereate instance/device proc getters.

Change-Id: I8498c711ee1fa1cded71e4a7a63317a4b125272b
Reviewed-on: https://skia-review.googlesource.com/14277
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
3 files changed