Relevant dEQP tests:
dEQP-GLES3.functional.fragment_out.basic.int.rg16i*
dEQP-GLES3.functional.fragment_out.basic.uint.rg16ui*
dEQP-GLES3.functional.fragment_out.basic.int.rgba16i*
dEQP-GLES3.functional.fragment_out.basic.uint.rgba16ui*

Change-Id: If57f6edb895c576f78cb4cdf6048c2063d884a6f
Reviewed-on: https://swiftshader-review.googlesource.com/5651Tested-by: Meng-Lin Wu <marleymoo@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>