Fixed "log enable linux registers" and added a test.

- Eliminated the use of static for methods that read m_register_infos, so that these routines can be implemented in the base class.
- Eliminated m_register_infos in the base class because this is not used when derived classes call UpdateRegisterInfo.
- Also moved the namespace using declarations from headers to source files.

Thanks to Daniel and Samuel for their review feedback.

llvm-svn: 181538