i965: Enable OES_texture_cube_map_array on Gen8+

i965: Enable OES_texture_cube_map_array on Gen8+

These are the only platforms that current expose OES_geometry_shader.
Once OpenGL ES 3.1 and OES_geometry_shader are enabled on Gen7, this
extension can be enabled there as well.

Gen6 will never get OpenGL ES 3.1, so it will never get this
extension... even though it has the desktop OpenGL extension.  Alas.

NOTE: This causes a failure on Gen8+ platforms in
ES3-CTS.gtf.GL3Tests.texture_storage.texture_storage_texture_targets.
The test only fails because it doesn't know that 0x9009 is a valid
value when the extension exists.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>