Implementation attempt for glInstanceID.
Related dEQP tests pass.

Change-Id: I6391699a127cc7c159a2a64e3ffeaa528b611f97
Reviewed-on: https://swiftshader-review.googlesource.com/3412Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>