fixup "PixelShaderGen: extract iround"
Revert "PixelShaderGen: extract imix"

This reverts commit 7fe64bb2a5e0073c30bf8d717962ef8e83a9c666.
fixup "ShaderGen/D3D: inline centroid"
fixup "ShaderGen: merge early-z blocks of ogl+d3d"