I6400 mips64r6 prip4

This pull request contains the following features required for I6400 emulation:
- Config5.FRE feature allowing emulation of Status.FR=0 on a 64-bit FPU with Status.FR=1.
- Config5.LLB feature which makes LLbit visible to the software through CP0.LLAddr[0], it also adds ERETNC instruction.
- Enable 48-bit Physical Address on MIPS64.
- Bug fixes