Use MRI::getSimpleHint() instead of getRegAllocPref() in remaining cases.

Targets can provide multiple hints now, so getRegAllocPref() doesn't
make sense any longer because it only returns one preferred register.
Replace it with getSimpleHint() in the remaining heuristics. This
function only

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169188 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed