boards: removed leading underscores from macros

* also added a trailing underscore to header guards for consistency

Commit for PR 2623, repairing header file include guards.
This PR is intended to fix the include guards in files under RIOT/boards

SQUASH ME: fix underscore removal overdos

SQUASH ME: consistent macro naming

SQUASH ME: missed that one

SQUASH ME: fixed overdo

SQUASH ME: consistency