mesa/main: do not allow s3tc enums on gles1

mesa/main: do not allow s3tc enums on gles1

There's no extension enabling S3TC formats on OpenGL ES 1.x, so we
shouldn't allow these even if the driver can support it. So let's check
for EXT_texture_compression_s3tc instead of ANGLE_texture_compression_dxt,
which is supported on all other OpenGL variations.

We also need to use _mesa_has_EXT_texture_compression_s3tc() instead of
checking the driver cap directly, otherwise we end up enabling this on
OpenGL ES 1.x, as the API isn't checked.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>