[PowerPC64LE] Add LOAD_LR_NIA and RETURN_TO_NATIVE_ENDIAN defines.
- Add LOAD_LR_NIA define. This is preferred to "bl 1f; 1:" because it
doesn't pollute the branch predictor.
- Add magic sequence to return the CPU to the correct endianness after
jumping to cross-endian code, similar to the sequence from Linux.
Sponsored by: Tag1 Consulting, Inc.