mesa: Only expose GLES's EXT_texture_type_2_10_10_10_REV if supported in HW.

mesa: Only expose GLES's EXT_texture_type_2_10_10_10_REV if supported in HW.

Previously, we were downconverting to 8888 automatically if the hardware
didn't suport it.  However, with the advent of
GL_OES_required_internalformat, we have to actually store the
internalformats we advertise support for.  And, it seems rather
disingenuous to advertise the extension if we don't actually support it.

v2: Throw an error when using the format on ES2 without the extension present.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>