Convert PhyRegAlloc into a proper pass.

PhyRegAlloc.cpp:
 Don't include TargetMachine.h or TargetRegInfo.h, because these are provided
  by PhyRegAlloc.h.
 Merge class RegisterAllocator into class PhyRegAlloc.
 Simplify & move ctor, dtor to PhyRegAlloc.h.
 Make some of PhyRegAlloc's reference members into pointer members,
  so they can be more easily messed with.
 MarkAllocatedRegs() becomes a member method, with fewer args.

PhyRegAlloc.h:
 Include Pass.h, TargetMachine.h and TargetRegInfo.h. Don't declare
  TargetRegInfo forward.
 Give AddedInstrns the obvious clear() method.
 Make some of PhyRegAlloc's reference members into pointer members,
  so they can be more easily messed with.
 Add prototype for markAllocatedRegs().
 Remove unused inline void constructLiveRanges().

llvm-svn: 8641