gallium: Make TGSI_SEMANTIC_FOG register four-component wide.
D3D9 Shader Model 2 restricted the fog register to one component, http://msdn.microsoft.com/en-us/library/windows/desktop/bb172945.aspx , but that restriction no longer exists in Shader Model 3, and several WHCK tests enforce that. So this change: - lifts the single-component restriction TGSI_SEMANTIC_FOG from Gallium interface - updates the Mesa state tracker to enforce output fog has (f, 0, 0, 1) - draw module was updated to leave TGSI_SEMANTIC_FOG output registers alone Several gallium drivers that are going out of their way to clear TGSI_SEMANTIC_FOG components could be simplified in the future. Thanks to Si Chen and Michal Krol for identifying the problem. Testing done: piglit fogcoord-*.vpfp tests Reviewed-by: Roland Scheidegger <firstname.lastname@example.org>
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