I have been debugging a weird issue in C2/deopt, and wanted to have stronger asserts in critical paths. One such place is `PhaseOutput::FillLocArray`, which emits `Location::normal` on unconditional `else` branch. `Location::normal` is described as "Ints, floats, double halves". I think we would be better off verifying the types explicitly. Same goes for `Location::oop`, which we can also verify.

Aside: In fact, I suspect the whole `Regalloc::is_oop` business can go away, and we can rely on reg types to sense if we are dealing with oops here, but that looks like a change with some unexpected effects, so I would like to do that separately, see JDK-8293845.