Code clean up.

- Use spin_lock_irqsave/irqrestore() according to other poll()
  implementation examples.
- Moved unused variables into comment block.
Remove manpage-related stuffs from Makefile.

- We can do "make install" now, which is required to use profiling tools
  such as perf with full symbol information.
Merge commit '407405452d79c85dc2a48d25612f4ff343d6a6fe'