freedreno: add fd_device_new_dup()

There seem to be some cases (I've noticed this switching resolution in
some games, for example) where the fd can get closed() before the device
and all it's bo's are destroyed.  Which, if the drm device is opened
again and bo's are allocated with the same handles, results that when
the first pipe_screen/pipe_context is destroyed causes the first dev to
close handles for bo's allocated by the second device.

The easy solution to that is to add a mode where the fd_device creates
it's own private fd (a dup()).

Signed-off-by: Rob Clark <robclark@freedesktop.org>