Failure is consistently seen in the dEQP tests on Windows 10 on
NVIDIA and Intel drivers, where creating an SRV from the buffer in the
right format fails. Disable the fast copy path for this format
similarly to how it's already disabled for some other formats.

BUG=angleproject:1095
TEST=dEQP-GLES3.functional.texture.specification.teximage2d_pbo.rgb5*

Change-Id: I7a1cd15c2cd130c9e8a637457c201778f157333b
Reviewed-on: https://chromium-review.googlesource.com/341170Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>