C2: Improve control of pinned loads split through phis to enable loop predication later

The fix attempt for JDK-8272574 relied on improving the load split through phi optimization by rewiring pinned loads less conservatively. This, however, was not done correctly (JDK-8277529). The fix for JDK-8277529 reverts the improved handling of JDK-8272574 because it did not fix the original root cause. This RFE should revisit the idea of JDK-8272574 to improve the control of pinned loads that are split through phis such that they do not end up between a loop and the predicates which prevents the application of loop predication.