We sometimes emulate depth-only or stencil-only buffers with depth-stencil
buffers. Disable depth-stencil states that allow reading or writing to these
buffers that should not exist.

BUG=angleproject:2739

Change-Id: I4f54800404f340eb53f04176e208f19a83a2899c
Reviewed-on: https://chromium-review.googlesource.com/1141932Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>