Cleanup deoptimization code to make it architecture independent (in progress).

runtime/vm/deopt_instructions.cc

Index: runtime/vm/deopt_instructions.cc
===================================================================
--- runtime/vm/deopt_instructions.cc	(revision 22345)
+++ runtime/vm/deopt_instructions.cc	(working copy)
@@ -40,12 +40,12 @@
 
 
 intptr_t DeoptimizationContext::GetFromFp() const {
-  return from_frame_[from_frame_size_ - 1 - num_args_ - 1];
+  return from_frame_[from_frame_size_ - num_args_ - kLastParamSlotIndex];
 }
 
 
 intptr_t DeoptimizationContext::GetFromPc() const {
-  return from_frame_[from_frame_size_ - 1 - num_args_];
+  return from_frame_[from_frame_size_ - num_args_ + kPcSlotIndexFromSp];
 }
 
 intptr_t DeoptimizationContext::GetCallerFp() const {