i965: Resolve implied moves in brw_dp_READ_4_vs_relative.
Fixes piglit test glsl-vs-arrays-3 on Sandybridge, as well as garbage rendering in 3DMarkMobileES 2.0's Taiji demo and GLBenchmark 2.0's Egypt and PRO demos. NOTE: This a candidate for stable release branches. It depends on commit 9a21bc64.