drm: qxl: Open code teardown function for qxl

This avoids using the deprecated drm_put_dev() and unload() hook
interfaces in the qxl driver.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Gustavo Padovan <gustavo.padovan@collabora.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170119134806.8926-2-krisman@collabora.co.uk