Since we don't expose the ASTC related extension string,
we need to hide support for ASTC related enums. ASTC_SUPPORT
was added to easily re-enable ASTC, should we want to.

Change-Id: I3c65906c4729df8a2efb1a9a78e155bccdc715f9
Reviewed-on: https://swiftshader-review.googlesource.com/13749Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>