imx: update is_imx6ull to include i.MX6ULZ
Update is_imx6ull helper to include i.MX6ULZ SoC. i.MX6ULZ could
share same macro, then we no need to add is_imx6ulz in various drivers.
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>