nvmem: imx-ocotp: add write support

Implement write routine for OCOTP controller found in i.MX6 SoC's.
Furthermore add locking to the read function to prevent race conditions.
The write routine code is based on the fsl_otp driver from Freescale.

Signed-off-by: Richard Leitner <richard.leitner@skidata.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>