* Keep track of register alignment as well as register size

* Add comments
* Add a new allocation_order iterator for register classes which targets may
  use to control the register order and available registers based on properties
  of the function being compiled.
* Remove access to FP and SP registers
* Add new callframe setup opcode support
* Eliminate moveImm2Reg method
* Revamp frame offset handling and prolog/epilog code generation

llvm-svn: 5167