Pass the shadow bo to qxl_io_create_primary() instead of expecting
qxl_io_create_primary to check bo->shadow.  Set is_primary flag on the
shadow bo.  Move the is_primary tracking into qxl_io_create_primary()
and qxl_io_destroy_primary() functions.

That simplifies primary surface tracking and the workflow in
qxl_primary_atomic_update().
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190118122020.27596-14-kraxel@redhat.com

qxl_io_create/destroy_primary: primary_bo tracking [fixup]