etnaviv: fix GLES2 texturing issues (GC2000/GC3000)

Merged Jonathan Marek requested to merge flto/mesa:etna-texture into master

This series includes patches to pass all dEQP-GLES2.functional.texture.* tests on GC2000/GC3000. Only exception is warnings in dEQP-GLES2.functional.texture.mipmap.cube.* because of sampling from wrong LOD for a corner pixel (looks like a HW problem?)

Edited by Jonathan Marek

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