This texture format is needed to run the PowerVR Glass demo

Bug: b/136178423
Tests: dEQP-VK.*r8_srgb*

Change-Id: Ifff800e25db69daf099ce9c748a6c16de6d93db1
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/33449Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Hernan Liatis <hliatis@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>