Some i.MX SoCs have GPIO clock gates in CCM CCGR, such as
i.MX6SLL, need to enable clocks before accessing GPIO
registers, add optional clock operation for GPIO driver.
Signed-off-by: NAnson Huang <Anson.Huang@nxp.com>
Reviewed-by: NFabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>