Provide missing OpenGL ES 1.x extension for implementation read format/type.

Bug 14643416

Change-Id: Ie710b76fcf1f64849a4f0556c3f0db587304000e
Reviewed-on: https://swiftshader-review.googlesource.com/1870
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>