MIPS: Refactor HType to get rid of various hacks.

Port r21578 (dcf13aa)

Original commit message:
- Move HType to it's own file.
- Add HType::HeapObject and some other useful types.
- Get rid of the broken and useless HType::NonPrimitive.
- Introduce HType::FromType() to convert from HeapType to HType.
- Also add unit tests for HType.
- Fix types in Crankshaft.

BUG=
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/301023004

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21580 ce2b1a6d-e550-0410-aec6-3dcde31c8c00