nvmem: imx-ocotp: remove nvmem regmap dependency

This patch moves to nvmem support in the driver to use callback
instead of regmap.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>