pan/midgard: Implement textureOffset for 2D textures
Fixes dEQP-GLES3.functional.shaders.texture_functions.textureoffset.sampler2d_fixed_fragment.
Later in the series we enable lowering for txd as well, so in short this means less crashes on dEQP-GLES3.
Edited by Alyssa Rosenzweig