panfrost: ZS texture sampling fixes
I got things wrong in !7922 (merged). According to the TGSI doc (section Texture Sampling and Texture Formats
in docs/gallium/tgsi.rst), depth and stencil components should be replicated on all components, and the simple TGSI shaders were correct.
Fix the panfrost driver so we can revert the faulty patch (requires some changes to Zink).
Edited by Boris Brezillon