[boards] moved native internal functions declarations (#12)

You can merge this Pull Request by running:

  git pull https://github.com/LudwigOrtmann/boards master

Or you can view, comment on it, or merge it online at:

  https://github.com/RIOT-OS/boards/pull/12

-- Commit Summary --

  * moved native internal functions declarations

-- File Changes --

    M native/board_init.c (2)     M native/drivers/native-uart0.c (2)     M native/include/board.h (6)     A native/include/board_internal.h (6)

-- Patch Links --

https://github.com/RIOT-OS/boards/pull/12.patch https://github.com/RIOT-OS/boards/pull/12.diff

Merged #12.