staging/xgifb: Needs to be converted to a drm driver

The fbdev subsystem is closed for new drivers, those need to become
drm ones (which generally results in smaller drivers nowadays, with
the massive amounts of shared infrastructure and helper libraries drm
has).

Although given the lack of progress since 2010, maybe time to ditch it
from staging outright?

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Arnaud Patard <arnaud.patard@rtp-net.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>