Introduce ocotp_ctrl_reg to include the low 16bits mask of CTRL
register.

i.MX chips will have different layout of the low 16bits of CTRL
register, so use ocotp_ctrl_reg will make it clean to add new
chip support.
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200109104017.6249-4-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>