Generalize the PassConfig API and remove addFinalizeRegAlloc().

The target hooks are getting out of hand. What does it mean to run
before or after regalloc anyway? Allowing either Pass* or AnalysisID
pass identification should make it much easier for targets to use the
substitutePass and insertPass APIs, and create less need for badly
named target hooks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179140 91177308-0d34-0410-b5e6-96231b3b80d8