FreeBSD. Add drm_get_resource_{start|len} so linux-specific stuff
doesn't need to be in shared code.
- Fix mach64 build by using __DECONST to work around passing a const
pointer to useracc, which is unfortunately not marked const.
- Get rid of a lot of maplist code by not having dev->maplist be a pointer,
and by sticking the link entries directly in drm_local_map_t rather
than having a separate structure for the linked list.
- Factor out map uninit and removal into its own routine, rather than
duplicating in both drm_takedown() and drm_rmmap().
- Hook up more driver functions, and correct FreeBSD-specific bits of
radeon_cp.c, making radeon work.
- Baby steps towards using bus_space as we should.
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.