nvmem: imx-ocotp: Add i.MX6 OCOTP driver

This driver handles the i.MX On-Chip OTP Controller found in
i.MX6Q/D, i.MX6S/DL, i.MX6SL, and i.MX6SX SoCs. Currently it
just returns the values stored in the shadow registers.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>