svga: adjust line subpixel position for HWv8
This fixes two regressions on HWv8: Piglit gl-1.0-ortho-pos Piglit/glean fbo This was caused by commit c2b92dad "svga: clamp device line width to at least 1 to fix HWv8 line stippling" This also fixes two conform tests: Vertex Order and Polygon Face No Piglit/conform changes with HWv9 or later. VMware bug 1905053 Reviewed-by:Charmaine Lee <charmainel@vmware.com>