Fix building for MacOSX.

- Add a new macro named IS_MACOSX to hwaccess.c and use it to enable iopl().
  This was broken since r1638. This fix does *not* restore the very permissive
  concept where iopl() was activated in an #else branch that was inplace before
  r1638.
- Make printing the image file's size in flashrom.c platform independent.

Bonus: remove definitions of off64_t and lseek64 which are not necessary
anymore for about 1000 commits.

Thanks to SJ for reporting the issue and testing the solution.

Signed-off-by: Stefan Tauner <stefan.tauner@student.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@student.tuwien.ac.at>

git-svn-id: svn://coreboot.org/flashrom/trunk@1648 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1