Also minor refactor to avoid duplicating the constant by having
both RendererVk and ContextVk retrieve the wait time via new
member function RendererVk::getMaxFenceWaitTimeNs().

BUG=angleproject:3915

Change-Id: I9a283a4e0f34a6a1f840c350dc667f4fc27f59e4
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1810066Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>