drm: rockchip: Turn off VT switching on suspend

drm/rockchip already has support for disabling all displays on suspend
and enabling them on resume.

Disable automatic VT switching on suspend by the pm console tracking
layer.

Tested on veyron, used `echo mem > sys/power/state`
  => verified no VT switch

Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>