drm/qxl: move qxl_primary_apply_cursor to correct place

The qxl device ties the cursor to the primary surface.  Therefore
calling qxl_io_destroy_primary() and qxl_io_create_primary() to switch
the framebuffer causes the cursor information being lost and the driver
must re-apply it.

The correct call order to do that is qxl_io_destroy_primary() +
qxl_io_create_primary() + qxl_primary_apply_cursor().

The old code did qxl_io_destroy_primary() + qxl_primary_apply_cursor() +
qxl_io_create_primary().  Due to qxl_primary_apply_cursor request being
queued in a ringbuffer and qxl_io_create_primary() trapping to the
hypervisor instantly there is a high chance that qxl_io_create_primary()
is processed first even with the wrong call order.  But it's racy and
thus not reliable.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190118122020.27596-11-kraxel@redhat.com