Commit first pieces of port to OpenBSD, done by Martin Lexa (martin at

    martinlexa dot cz). Now that we've got porting for all three major BSDs
    (and the fourth being very similar to FreeBSD), move the
    mostly-duplication drm_os_* files into drmP.h. Remove some cruft from
    linux heritage and from pieces of the DRM that have since been removed.
Note that things are still not quite working for even FreeBSD, but these
    are first steps at cleanup, and just a WIP checkpoint.