Link to vulkan in tools but not library.

This also now requires an explicit vulkan proc address getter to be used with GrVkBackendContext::Create.

Change-Id: I768ec487398dab68e6e10409419ac7a00ec1822a
Reviewed-on: https://skia-review.googlesource.com/14322
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
3 files changed