switched GrVkPipelineStateCache over to use SkLRUCache

BUG=skia:

Change-Id: I04301313132df170a16995b4830b13ffbddbed3b
Reviewed-on: https://skia-review.googlesource.com/6469
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
4 files changed