Add a VT argument to getMinimalPhysRegClass and replace the copy related uses

Add a VT argument to getMinimalPhysRegClass and replace the copy related uses
of getPhysicalRegisterRegClass with it.

If we want to make a copy (or estimate its cost), it is better to use the
smallest class as more efficient operations might be possible.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@107140 91177308-0d34-0410-b5e6-96231b3b80d8