[AArch64] Make AArch64A57FPLoadBalancing output stable.

Add tie breaker to colorChainSet() sort so that processing order doesn't
depend on std::set order, which depends on pointer order, which is
unstable from run to run.

No test case as this is nearly impossible to reproduce.

Phabricator Review: http://reviews.llvm.org/D7265
Patch by Geoff Berry <gberry@codeaurora.org>!

llvm-svn: 227606