Allow these transforms for types like i256 while

Allow these transforms for types like i256 while
still excluding types like i1 (not byte sized)
and i120 (loading an i120 requires loading an i64,
an i32, an i16 and an i8, which is expensive).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52310 91177308-0d34-0410-b5e6-96231b3b80d8