(1) Change the way unused regs. are marked and found to consider regType

(1) Change the way unused regs. are marked and found to consider regType
    info (since multiple reg types may share the same reg class).
(2) Remove machine-specific regalloc. methods that are no longer needed.
    In particular, arguments and return value from a call do not need
    machine-specific code for allocation.
(3) Rename TargetRegInfo::getRegType variants to avoid unintentional
    overloading when an include file is omitted.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7329 91177308-0d34-0410-b5e6-96231b3b80d8