No support for non-zero mipmaps as sources yet.

Suppress dEQP tests due to apparent driver bugs with scissored clears on depth
or stencil attachments.

BUG=angleproject:2668

Change-Id: Idaa5e70ce9b0c91232fbb989cbf4de1b9134aafb
Reviewed-on: https://chromium-review.googlesource.com/c/1415010
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>