drm: qxl: Let DRM core handle connector registering

Registering the connector explicitly right after creation is not
necessary for modesetting drivers, because drm_dev_register already takes
care of this on the core side, by calling drm_modeset_register_all.

In addition, performing the initialization too early will get in the way
of the load() hook removal, because the connector interface cannot be
published prior to registering the minors.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
CC: Dave Airlie <airlied@redhat.com>
CC: Daniel Vetter <daniel.vetter@ffwll.ch>
CC: dri-devel@lists.freedesktop.org
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170112161610.19924-1-krisman@collabora.co.uk